diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index 25a27be..972ad2a 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -39,6 +39,12 @@
 #endif
 
 #if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
+
+#if !defined(unix) && !defined(__unix__) && !defined(__unix) && \
+    !defined(__APPLE__) && !defined(_WIN32)
+#error "Platform entropy sources only work on Unix and Windows, see MBEDTLS_NO_PLATFORM_ENTROPY in config.h"
+#endif
+
 #if defined(_WIN32) && !defined(EFIX64) && !defined(EFI32)
 
 #if !defined(_WIN32_WINNT)