diff --git a/include/cubescript/cubescript/callable.hh b/include/cubescript/cubescript/callable.hh
index 24a8dd7..0cb5f62 100644
--- a/include/cubescript/cubescript/callable.hh
+++ b/include/cubescript/cubescript/callable.hh
@@ -10,6 +10,7 @@
 #ifndef LIBCUBESCRIPT_CUBESCRIPT_CALLABLE_HH
 #define LIBCUBESCRIPT_CUBESCRIPT_CALLABLE_HH
 
+#include <cstring>
 #include <cstddef>
 #include <utility>
 #include <type_traits>
diff --git a/include/cubescript/cubescript/error.hh b/include/cubescript/cubescript/error.hh
index da175ec..58fe24e 100644
--- a/include/cubescript/cubescript/error.hh
+++ b/include/cubescript/cubescript/error.hh
@@ -13,8 +13,6 @@
 #include <string_view>
 #include <stdexcept>
 #include <utility>
-#include <cstdlib>
-#include <cstring>
 
 namespace cubescript {
 
@@ -108,6 +106,9 @@ struct LIBCUBESCRIPT_EXPORT error {
         p_stack{std::move(v.p_stack)}
     {}
 
+    /** @brief Construct an error using a string. */
+    error(state &cs, std::string_view msg);
+
     /** @brief Get a view of the error message. */
     std::string_view what() const {
         return std::string_view{p_errbeg, std::size_t(p_errend - p_errbeg)};
@@ -122,45 +123,10 @@ struct LIBCUBESCRIPT_EXPORT error {
     stack_state const &stack() const {
         return p_stack;
     }
-
-    /** @brief Construct an error using an unformatted string. */
-    error(state &cs, std::string_view msg):
-        p_errbeg{}, p_errend{}, p_stack{cs}
-    {
-        char *sp;
-        char *buf = request_buf(cs, msg.size(), sp);
-        std::memcpy(buf, msg.data(), msg.size());
-        buf[msg.size()] = '\0';
-        p_errbeg = sp;
-        p_errend = buf + msg.size();
-        p_stack = save_stack(cs);
-    }
-
-    /** @brief Construct an error using a `printf`-style format string. */
-    template<typename ...A>
-    error(state &cs, std::string_view msg, A const &...args):
-        p_errbeg{}, p_errend{}, p_stack{cs}
-    {
-        std::size_t sz = msg.size() + 64;
-        char *buf, *sp;
-        for (;;) {
-            buf = request_buf(cs, sz, sp);
-            int written = std::snprintf(buf, sz, msg.data(), args...);
-            if (written <= 0) {
-                throw error{cs, "malformed format string"};
-            } else if (std::size_t(written) <= sz) {
-                break;
-            }
-            sz = std::size_t(written);
-        }
-        p_errbeg = sp;
-        p_errend = buf + sz;
-        p_stack = save_stack(cs);
-    }
-
 private:
-    stack_state save_stack(state &cs);
-    char *request_buf(state &cs, std::size_t bufs, char *&sp);
+    friend struct error_p;
+
+    error(state &cs, char const *errbeg, char const *errend);
 
     char const *p_errbeg, *p_errend;
     stack_state p_stack;
diff --git a/src/cs_error.cc b/src/cs_error.cc
index 2dd0a49..c0a9252 100644
--- a/src/cs_error.cc
+++ b/src/cs_error.cc
@@ -4,6 +4,7 @@
 #include <algorithm>
 
 #include "cs_thread.hh"
+#include "cs_error.hh"
 
 namespace cubescript {
 
@@ -44,46 +45,7 @@ LIBCUBESCRIPT_EXPORT bool stack_state::gap() const {
     return p_gap;
 }
 
-LIBCUBESCRIPT_EXPORT char *error::request_buf(
-    state &cs, std::size_t bufs, char *&sp
-) {
-    auto &ts = state_p{cs}.ts();
-    charbuf &cb = ts.errbuf;
-    cb.clear();
-    std::size_t sz = 0;
-    if (ts.current_line) {
-        /* we can attach line number */
-        sz = ts.source.size() + 32;
-        for (;;) {
-            /* we are using so the buffer tracks the elements and therefore
-             * does not wipe them when we attempt to reserve more capacity
-             */
-            cb.resize(sz);
-            int nsz;
-            if (!ts.source.empty()) {
-                nsz = std::snprintf(
-                    cb.data(), sz, "%.*s:%zu: ",
-                    int(ts.source.size()), ts.source.data(),
-                    *ts.current_line
-                );
-            } else {
-                nsz = std::snprintf(cb.data(), sz, "%zu: ", *ts.current_line);
-            }
-            if (nsz <= 0) {
-                abort(); /* should be unreachable */
-            } else if (std::size_t(nsz) < sz) {
-                sz = std::size_t(nsz);
-                break;
-            }
-            sz = std::size_t(nsz + 1);
-        }
-    }
-    cb.resize(sz + bufs + 1);
-    sp = cb.data();
-    return &cb[sz];
-}
-
-LIBCUBESCRIPT_EXPORT stack_state error::save_stack(state &cs) {
+static stack_state save_stack(state &cs) {
     auto &ts = state_p{cs}.ts();
     builtin_var *dalias = ts.istate->ivar_dbgalias;
     auto dval = std::clamp(
@@ -124,4 +86,22 @@ LIBCUBESCRIPT_EXPORT stack_state error::save_stack(state &cs) {
     return stack_state{cs, ret, total > dval};
 }
 
+LIBCUBESCRIPT_EXPORT error::error(state &cs, std::string_view msg):
+    p_errbeg{}, p_errend{}, p_stack{cs}
+{
+    char *sp;
+    char *buf = state_p{cs}.ts().request_errbuf(msg.size(), sp);
+    std::memcpy(buf, msg.data(), msg.size());
+    buf[msg.size()] = '\0';
+    p_errbeg = sp;
+    p_errend = buf + msg.size();
+    p_stack = save_stack(cs);
+}
+
+LIBCUBESCRIPT_EXPORT error::error(
+    state &cs, char const *errbeg, char const *errend
+): p_errbeg{errbeg}, p_errend{errend}, p_stack{cs} {
+    p_stack = save_stack(cs);
+}
+
 } /* namespace cubescript */
diff --git a/src/cs_ident.cc b/src/cs_ident.cc
index cb99445..8771870 100644
--- a/src/cs_ident.cc
+++ b/src/cs_ident.cc
@@ -3,6 +3,7 @@
 #include "cs_bcode.hh"
 #include "cs_thread.hh"
 #include "cs_vm.hh"
+#include "cs_error.hh"
 
 namespace cubescript {
 
@@ -229,10 +230,10 @@ LIBCUBESCRIPT_EXPORT void builtin_var::save(state &cs) {
     auto &ts = state_p{cs}.ts();
     if ((ts.ident_flags & IDENT_FLAG_OVERRIDDEN) || is_overridable()) {
         if (p_impl->p_flags & IDENT_FLAG_PERSIST) {
-            throw error{
+            throw error_p::make(
                 cs, "cannot override persistent variable '%s'",
                 name().data()
-            };
+            );
         }
         if (!(p_impl->p_flags & IDENT_FLAG_OVERRIDDEN)) {
             auto *imp = static_cast<var_impl *>(p_impl);
@@ -293,9 +294,9 @@ LIBCUBESCRIPT_EXPORT void builtin_var::set_value(
     state &cs, any_value val, bool do_write, bool trigger
 ) {
     if (is_read_only()) {
-        throw error{
+        throw error_p::make(
             cs, "variable '%s' is read only", name().data()
-        };
+        );
     }
     if (!do_write) {
         return;
@@ -375,7 +376,7 @@ LIBCUBESCRIPT_EXPORT any_value command::call(
 
 LIBCUBESCRIPT_EXPORT alias_local::alias_local(state &cs, ident &a) {
     if (a.type() != ident_type::ALIAS) {
-        throw error{cs, "ident '%s' is not an alias", a.name().data()};
+        throw error_p::make(cs, "ident '%s' is not an alias", a.name().data());
     }
     auto &ts = state_p{cs}.ts();
     p_alias = static_cast<alias *>(&a);
diff --git a/src/cs_parser.cc b/src/cs_parser.cc
index 31fc5d9..9e370cb 100644
--- a/src/cs_parser.cc
+++ b/src/cs_parser.cc
@@ -6,6 +6,7 @@
 #include <iterator>
 
 #include "cs_parser.hh"
+#include "cs_error.hh"
 
 namespace cubescript {
 
@@ -56,9 +57,9 @@ LIBCUBESCRIPT_EXPORT char const *parse_string(
 end:
     nlines = nl;
     if ((beg == end) || (*beg != '\"')) {
-        throw error{
+        throw error_p::make(
             cs, "unfinished string '%.*s'", int(beg - orig), orig
-        };
+        );
     }
     return ++beg;
 }
@@ -1116,7 +1117,9 @@ static bool finish_statement(parser_state &ps, bool more, int term) {
         /* EOS */
         case '\0':
             if (ps.current() != term) {
-                throw error{*ps.ts.pstate, "missing \"%c\"", char(term)};
+                throw error_p::make(
+                    *ps.ts.pstate, "missing \"%c\"", char(term)
+                );
             }
             return false;
         /* terminating parens/brackets */
@@ -1127,7 +1130,9 @@ static bool finish_statement(parser_state &ps, bool more, int term) {
                 ps.next_char();
                 return false;
             }
-            throw error{*ps.ts.pstate, "unexpected \"%c\"", ps.current()};
+            throw error_p::make(
+                *ps.ts.pstate, "unexpected \"%c\"", ps.current()
+            );
         /* potential comment */
         case '/':
             ps.next_char();
diff --git a/src/cs_state.cc b/src/cs_state.cc
index 7296297..7077d88 100644
--- a/src/cs_state.cc
+++ b/src/cs_state.cc
@@ -8,6 +8,7 @@
 #include "cs_strman.hh"
 #include "cs_vm.hh" // break/continue, call_with_args
 #include "cs_parser.hh"
+#include "cs_error.hh"
 
 namespace cubescript {
 
@@ -58,9 +59,9 @@ ident &internal_state::new_ident(state &cs, std::string_view name, int flags) {
     ident *id = get_ident(name);
     if (!id) {
         if (!is_valid_name(name)) {
-            throw error{
+            throw error_p::make(
                 cs, "'%s' is not a valid identifier name", name.data()
-            };
+            );
         }
         auto *inst = create<alias_impl>(
             cs, string_ref{cs, name}, flags
@@ -392,14 +393,14 @@ static void var_name_check(
     state &cs, ident *id, std::string_view n
 ) {
     if (id) {
-        throw error{
+        throw error_p::make(
             cs, "redefinition of ident '%.*s'", int(n.size()), n.data()
-        };
+        );
     } else if (!is_valid_name(n)) {
-        throw error{
+        throw error_p::make(
             cs, "'%.*s' is not a valid variable name",
             int(n.size()), n.data()
-        };
+        );
     }
 }
 
@@ -472,13 +473,15 @@ LIBCUBESCRIPT_EXPORT void state::assign_value(
                 id->get().call(span_type<any_value>{&v, 1}, *this);
                 break;
             default:
-                throw error{
+                throw error_p::make(
                     *this, "cannot redefine builtin %s with an alias",
                     id->get().name().data()
-                };
+                );
         }
     } else if (!is_valid_name(name)) {
-        throw error{*this, "cannot alias invalid name '%s'", name.data()};
+        throw error_p::make(
+            *this, "cannot alias invalid name '%s'", name.data()
+        );
     } else {
         auto *a = p_tstate->istate->create<alias_impl>(
             *this, string_ref{*this, name}, std::move(v),
@@ -531,17 +534,21 @@ LIBCUBESCRIPT_EXPORT any_value state::lookup_value(std::string_view name) {
                 return any_value{};
         }
     }
-    throw error{*this, "unknown alias lookup: %s", name.data()};
+    throw error_p::make(*this, "unknown alias lookup: %s", name.data());
 }
 
 LIBCUBESCRIPT_EXPORT void state::reset_value(std::string_view name) {
     auto id = get_ident(name);
     if (!id) {
-        throw error{*this, "variable '%s' does not exist", name.data()};
+        throw error_p::make(
+            *this, "variable '%s' does not exist", name.data()
+        );
     }
     if (id->get().type() == ident_type::VAR) {
         if (static_cast<builtin_var &>(id->get()).is_read_only()) {
-            throw error{*this, "variable '%s' is read only", name.data()};
+            throw error_p::make(
+                *this, "variable '%s' is read only", name.data()
+            );
         }
     }
     clear_override(id->get());
@@ -619,9 +626,9 @@ LIBCUBESCRIPT_EXPORT command &state::new_command(
                 fmt += 2;
                 break;
             default:
-                throw error{
+                throw error_p::make(
                     *this, "invalid argument type: %c", *fmt
-                };
+                );
         }
     }
     auto &is = *p_tstate->istate;
@@ -653,18 +660,18 @@ LIBCUBESCRIPT_EXPORT command &state::new_command(
         }
         /* we haven't found one matching the list, so error */
         is.destroy(cmd);
-        throw error{
+        throw error_p::make(
             *this, "forbidden builtin command: %.*s",
             int(name.size()), name.data()
-        };
+        );
     }
 valid:
     if (is.get_ident(name)) {
         is.destroy(cmd);
-        throw error{
+        throw error_p::make(
             *this, "redefinition of ident '%.*s'",
             int(name.size()), name.data()
-        };
+        );
     }
 do_add:
     is.add_ident(cmd, cmd);
diff --git a/src/cs_thread.cc b/src/cs_thread.cc
index 1eefca5..533be32 100644
--- a/src/cs_thread.cc
+++ b/src/cs_thread.cc
@@ -1,5 +1,7 @@
 #include "cs_thread.hh"
 
+#include <cstdio>
+
 namespace cubescript {
 
 thread_state::thread_state(internal_state *cs):
@@ -27,4 +29,41 @@ alias_stack &thread_state::get_astack(alias const *a) {
     return it.first->second;
 }
 
+char *thread_state::request_errbuf(std::size_t bufs, char *&sp) {
+    errbuf.clear();
+    std::size_t sz = 0;
+    if (current_line) {
+        /* we can attach line number */
+        sz = source.size() + 32;
+        for (;;) {
+            /* we are using so the buffer tracks the elements and therefore
+             * does not wipe them when we attempt to reserve more capacity
+             */
+            errbuf.resize(sz);
+            int nsz;
+            if (!source.empty()) {
+                nsz = std::snprintf(
+                    errbuf.data(), sz, "%.*s:%zu: ",
+                    int(source.size()), source.data(),
+                    *current_line
+                );
+            } else {
+                nsz = std::snprintf(
+                    errbuf.data(), sz, "%zu: ", *current_line
+                );
+            }
+            if (nsz <= 0) {
+                abort(); /* should be unreachable */
+            } else if (std::size_t(nsz) < sz) {
+                sz = std::size_t(nsz);
+                break;
+            }
+            sz = std::size_t(nsz + 1);
+        }
+    }
+    errbuf.resize(sz + bufs + 1);
+    sp = errbuf.data();
+    return &errbuf[sz];
+}
+
 } /* namespace cubescript */
diff --git a/src/cs_thread.hh b/src/cs_thread.hh
index e64605a..6899cdc 100644
--- a/src/cs_thread.hh
+++ b/src/cs_thread.hh
@@ -53,6 +53,8 @@ struct thread_state {
     hook_func const &get_hook() const { return call_hook; }
 
     alias_stack &get_astack(alias const *a);
+
+    char *request_errbuf(std::size_t bufs, char *&sp);
 };
 
 } /* namespace cubescript */
diff --git a/src/cs_vm.cc b/src/cs_vm.cc
index 1051389..f25c7c8 100644
--- a/src/cs_vm.cc
+++ b/src/cs_vm.cc
@@ -2,6 +2,7 @@
 #include "cs_vm.hh"
 #include "cs_std.hh"
 #include "cs_parser.hh"
+#include "cs_error.hh"
 
 #include <cstdio>
 #include <cmath>
@@ -149,9 +150,9 @@ bool exec_alias(
             return false;
         }
     } else if (aast.flags & IDENT_FLAG_UNKNOWN) {
-        throw error {
+        throw error_p::make(
             *ts.pstate, "unknown command: %s", a->name().data()
-        };
+        );
     }
     /* excess arguments get ignored (make error maybe?) */
     callargs = std::min(callargs, MAX_ARGUMENTS);
@@ -237,9 +238,9 @@ static inline alias *get_lookup_id(
     } else {
         ast = &ts.get_astack(static_cast<alias *>(id));
         if (ast->flags & IDENT_FLAG_UNKNOWN) {
-            throw error{
+            throw error_p::make(
                 *ts.pstate, "unknown alias lookup: %s", id->name().data()
-            };
+            );
         }
     }
     return static_cast<alias *>(id);
@@ -799,9 +800,9 @@ noid:
                     result.force_none();
                     force_arg(cs, result, op & BC_INST_RET_MASK);
                     std::string_view ids{idn};
-                    throw error{
+                    throw error_p::make(
                         cs, "unknown command: %s", ids.data()
-                    };
+                    );
                 }
                 result.force_none();
                 switch (ident_p{id->get()}.impl().p_type) {
diff --git a/src/lib_base.cc b/src/lib_base.cc
index 8d61949..4d3545c 100644
--- a/src/lib_base.cc
+++ b/src/lib_base.cc
@@ -5,6 +5,7 @@
 #include "cs_std.hh"
 #include "cs_ident.hh"
 #include "cs_thread.hh"
+#include "cs_error.hh"
 
 namespace cubescript {
 
@@ -72,10 +73,10 @@ LIBCUBESCRIPT_EXPORT void std_init_base(state &gcs) {
         auto &cret = args[1].get_ident(cs);
         auto &css = args[2].get_ident(cs);
         if (cret.type() != ident_type::ALIAS) {
-            throw error{cs, "'%s' is not an alias", cret.name().data()};
+            throw error_p::make(cs, "'%s' is not an alias", cret.name().data());
         }
         if (css.type() != ident_type::ALIAS) {
-            throw error{cs, "'%s' is not an alias", css.name().data()};
+            throw error_p::make(cs, "'%s' is not an alias", css.name().data());
         }
         any_value result{}, tback{};
         bool rc = true;
@@ -98,6 +99,25 @@ LIBCUBESCRIPT_EXPORT void std_init_base(state &gcs) {
         ts.get_astack(ssa).set_alias(ssa, ts, tback);
     });
 
+    new_cmd_quiet(gcs, "assert", "ss#", [](auto &s, auto args, auto &ret) {
+        auto val = args[0];
+        val.force_code(s);
+        if (!val.get_code().call(s).get_bool()) {
+            if (args[2].get_integer() > 1) {
+                throw error_p::make(
+                    s, "assertion failed: [%s] (%s)",
+                    args[0].get_string(s).data(), args[1].get_string(s).data()
+                );
+            } else {
+                throw error_p::make(
+                    s, "assertion failed: [%s]",
+                    args[0].get_string(s).data()
+                );
+            }
+        }
+        ret = std::move(args[0]);
+    });
+
     new_cmd_quiet(gcs, "?", "aaa", [](auto &, auto args, auto &res) {
         if (args[0].get_bool()) {
             res = std::move(args[1]);
@@ -343,7 +363,7 @@ end:
     new_cmd_quiet(gcs, "getalias", "s", [](auto &cs, auto args, auto &res) {
         auto &id = cs.new_ident(args[0].get_string(cs));
         if (id.type() != ident_type::ALIAS) {
-            throw error{cs, "'%s' is not an alias", id.name().data()};
+            throw error_p::make(cs, "'%s' is not an alias", id.name().data());
         }
         if (ident_p{id}.impl().p_flags & IDENT_FLAG_UNKNOWN) {
             return;
diff --git a/tests/runner.cc b/tests/runner.cc
index b329592..02eb605 100644
--- a/tests/runner.cc
+++ b/tests/runner.cc
@@ -58,26 +58,6 @@ int main(int argc, char **argv) {
         throw skip_test{};
     });
 
-    /* takes a string so we can print it */
-    gcs.new_command("assert", "ss#", [](auto &s, auto args, auto &ret) {
-        auto val = args[0];
-        val.force_code(s);
-        if (!val.get_code().call(s).get_bool()) {
-            if (args[2].get_integer() > 1) {
-                throw cs::error{
-                    s, "assertion failed: [%s] (%s)",
-                    args[0].get_string(s).data(), args[1].get_string(s).data()
-                };
-            } else {
-                throw cs::error{
-                    s, "assertion failed: [%s]",
-                    args[0].get_string(s).data()
-                };
-            }
-        }
-        ret = std::move(args[0]);
-    });
-
     try {
         do_exec_file(gcs, argv[1]);
     } catch (skip_test) {
diff --git a/tools/repl.cc b/tools/repl.cc
index 5d0ad10..3331bfb 100644
--- a/tools/repl.cc
+++ b/tools/repl.cc
@@ -360,9 +360,11 @@ int main(int argc, char **argv) {
         cs::any_value val{};
         bool ret = do_exec_file(css, file, val);
         if (!ret) {
-            throw cs::error(
-                css, "could not execute file \"%s\"", file.data()
+            char buf[4096];
+            std::snprintf(
+                buf, sizeof(buf), "could not execute file \"%s\"", file.data()
             );
+            throw cs::error(css, buf);
         }
     });