diff --git a/e_os.h b/e_os.h
index 914a2bf..49a0c3e 100644
--- a/e_os.h
+++ b/e_os.h
@@ -13,6 +13,7 @@
 # include <openssl/opensslconf.h>
 
 # include <openssl/e_os2.h>
+# include <openssl/crypto.h>
 /*
  * <openssl/e_os2.h> contains what we can justify to make visible to the
  * outside; this file e_os.h is not part of the exported interface.
@@ -544,6 +545,23 @@
 # define CRYPTO_memcmp memcmp
 #endif
 
+#ifdef NDEBUG
+# define ossl_assert(x) (int)(x)
+#else
+__owur static ossl_inline int ossl_assert_int(int expr, const char *exprstr,
+                                              const char *file, int line)
+{
+    if (!expr)
+        OPENSSL_die(exprstr, file, line);
+
+    return expr;
+}
+
+# define ossl_assert(x) ossl_assert_int((int)(x), "Assertion failed: "#x, \
+                                         __FILE__, __LINE__)
+
+#endif
+
 #ifdef  __cplusplus
 }
 #endif