diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index f90167c..bc71307 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -75,7 +75,7 @@
     return 0;
 }
 #else /* !_WIN32_WINNT_WINXP */
-#error Entropy not available before Windows XP, use MBEDTLS_NO_PLATFORM_ENTROPY
+#error "Entropy not available before Windows XP, use MBEDTLS_NO_PLATFORM_ENTROPY"
 #endif /* !_WIN32_WINNT_WINXP */
 #else /* _WIN32 && !EFIX64 && !EFI32 */