diff --git a/ostd/process.hh b/ostd/process.hh
index e809a93..fdd06a8 100644
--- a/ostd/process.hh
+++ b/ostd/process.hh
@@ -21,6 +21,11 @@
 #include <vector>
 
 #include "ostd/platform.hh"
+
+#if !defined(OSTD_PLATFORM_POSIX) && !defined(OSTD_PLATFORM_WIN32)
+#  error "Unsupported platform"
+#endif
+
 #include "ostd/string.hh"
 #include "ostd/range.hh"
 #include "ostd/io.hh"
diff --git a/ostd/stream.hh b/ostd/stream.hh
index 12b5b03..01e954b 100644
--- a/ostd/stream.hh
+++ b/ostd/stream.hh
@@ -42,11 +42,16 @@
 #include <stdexcept>
 #include <system_error>
 
+#include "ostd/platform.hh"
+
+#if !defined(OSTD_PLATFORM_POSIX) && !defined(OSTD_PLATFORM_WIN32)
+#  error "Unsupported platform"
+#endif
+
 #ifndef OSTD_PLATFORM_WIN32
 #include <sys/types.h>
 #endif
 
-#include "ostd/platform.hh"
 #include "ostd/range.hh"
 #include "ostd/string.hh"
 #include "ostd/format.hh"