diff --git a/src/mbedtls/engine.c b/src/mbedtls/engine.c
index 2a6b8cf..2402ab2 100644
--- a/src/mbedtls/engine.c
+++ b/src/mbedtls/engine.c
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 
+#include <assert.h>
 #include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>