diff --git a/crypto/pem/pem2.h b/crypto/pem/pem2.h
index 4e484bcd82a5b695699878cbeedeea6421a27914..f31790d69cb038572233410489f0de10ac38242b 100644
--- a/crypto/pem/pem2.h
+++ b/crypto/pem/pem2.h
@@ -61,7 +61,9 @@
 extern "C" {
 #endif
 
+#ifndef HEADER_PEM_H
 void ERR_load_PEM_strings(void);
+#endif
 
 #ifdef __cplusplus
 }