diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index 2fb26fd..6242983 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -792,7 +792,7 @@
 int mbedtls_x509_crt_flush_cache( mbedtls_x509_crt const *crt );
 
 static inline int mbedtls_x509_crt_frame_acquire( mbedtls_x509_crt const *crt,
-                                                  mbedtls_x509_crt_frame **frame_ptr )
+                                                  mbedtls_x509_crt_frame const **frame_ptr )
 {
     int ret;
 #if defined(MBEDTLS_THREADING_C)