diff --git a/include/cubescript/cubescript/error.hh b/include/cubescript/cubescript/error.hh
index fc369d4..7fdfcd8 100644
--- a/include/cubescript/cubescript/error.hh
+++ b/include/cubescript/cubescript/error.hh
@@ -20,15 +20,6 @@ namespace cubescript {
 
 struct state;
 
-/** @brief An internal Cubescript error.
- *
- * This is an error that is never expected; it is thrown
- * when some API call fails due to most likely a bug.
- */
-struct internal_error: std::runtime_error {
-    using std::runtime_error::runtime_error;
-};
-
 /** @brief Represents the simplified call stack at a point in time.
  *
  * This is a simplified call stack; it is generally carried by errors
@@ -156,7 +147,7 @@ struct LIBCUBESCRIPT_EXPORT error {
             buf = request_buf(cs, sz, sp);
             int written = std::snprintf(buf, sz, msg.data(), args...);
             if (written <= 0) {
-                throw internal_error{"format error"};
+                throw error{cs, "malformed format string"};
             } else if (std::size_t(written) <= sz) {
                 break;
             }
diff --git a/src/cs_error.cc b/src/cs_error.cc
index 87994ed..acba612 100644
--- a/src/cs_error.cc
+++ b/src/cs_error.cc
@@ -1,5 +1,6 @@
 #include <cubescript/cubescript.hh>
 
+#include <cstdlib>
 #include <algorithm>
 
 #include "cs_thread.hh"
@@ -69,7 +70,7 @@ LIBCUBESCRIPT_EXPORT char *error::request_buf(
                 nsz = std::snprintf(cb.data(), sz, "%zu: ", *ts.current_line);
             }
             if (nsz <= 0) {
-                throw internal_error{"format error"};
+                abort(); /* should be unreachable */
             } else if (std::size_t(nsz) < sz) {
                 sz = std::size_t(nsz);
                 break;
diff --git a/src/cs_strman.cc b/src/cs_strman.cc
index 7273c22..4dc0621 100644
--- a/src/cs_strman.cc
+++ b/src/cs_strman.cc
@@ -1,3 +1,4 @@
+#include <cassert>
 #include <cubescript/cubescript.hh>
 
 #include "cs_strman.hh"
@@ -70,10 +71,14 @@ void string_pool::unref(char const *ptr) {
          */
         auto sr = std::string_view{ptr, ss->length};
         auto it = counts.find(sr);
+        /* this should *never* happen unless we have a bug */
+#ifndef NDEBUG
+        assert(it != counts.end());
+#else
         if (it == counts.end()) {
-            /* internal error: this should *never* happen */
-            throw internal_error{"no refcount"};
+            abort();
         }
+#endif
         /* we're freeing the key */
         counts.erase(it);
         /* dealloc */
diff --git a/src/cs_val.cc b/src/cs_val.cc
index 22d16d9..77ebbeb 100644
--- a/src/cs_val.cc
+++ b/src/cs_val.cc
@@ -5,6 +5,7 @@
 #include "cs_strman.hh"
 
 #include <cmath>
+#include <cstdlib>
 #include <iterator>
 
 namespace cubescript {
@@ -22,7 +23,7 @@ static std::string_view intstr(integer_type v, charbuf &buf) {
         }
     }
     if (n <= 0) {
-        throw internal_error{"format error"};
+        abort(); /* unreachable, provided a well-formed format string */
     }
     return std::string_view{buf.data(), std::size_t(n)};
 }
@@ -50,7 +51,7 @@ static std::string_view floatstr(float_type v, charbuf &buf) {
         }
     }
     if (n <= 0) {
-        throw internal_error{"format error"};
+        abort(); /* unreachable, provided a well-formed format string */
     }
     return std::string_view{buf.data(), std::size_t(n)};
 }
diff --git a/src/lib_str.cc b/src/lib_str.cc
index ec438bb..9031f33 100644
--- a/src/lib_str.cc
+++ b/src/lib_str.cc
@@ -1,3 +1,4 @@
+#include <cstdlib>
 #include <functional>
 #include <iterator>
 
@@ -148,8 +149,8 @@ LIBCUBESCRIPT_EXPORT void std_init_string(state &cs) {
             res.set_string(static_cast<char const *>(buf), ccs);
             return;
         }
-        /* should pretty much be unreachable */
-        throw internal_error{"format error"};
+        /* should be unreachable */
+        abort();
     });
 
     new_cmd_quiet(cs, "substr", "sii#", [](auto &ccs, auto args, auto &res) {