diff --git a/include/mbedtls/bn_mul.h b/include/mbedtls/bn_mul.h
index 80e4b38..dbdc0a3 100644
--- a/include/mbedtls/bn_mul.h
+++ b/include/mbedtls/bn_mul.h
@@ -38,6 +38,12 @@
 #ifndef MBEDTLS_BN_MUL_H
 #define MBEDTLS_BN_MUL_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include "bignum.h"
 
 #if defined(MBEDTLS_HAVE_ASM)