diff --git a/modules/openapi-generator/src/main/resources/C-libcurl/apiClient.h.mustache b/modules/openapi-generator/src/main/resources/C-libcurl/apiClient.h.mustache
index 034205fc2481..26e40c3627bb 100644
--- a/modules/openapi-generator/src/main/resources/C-libcurl/apiClient.h.mustache
+++ b/modules/openapi-generator/src/main/resources/C-libcurl/apiClient.h.mustache
@@ -69,6 +69,6 @@ char *strReplace(char *orig, char *rep, char *with);
 
 char *base64encode(const void *b64_encode_this, int encode_this_many_bytes);
 
-char *base64decode(const void *b64_decode_this, int decode_this_many_bytes);
+char *base64decode (const void *b64_decode_this, int decode_this_many_bytes, int *decoded_bytes);
 
 #endif // INCLUDE_API_CLIENT_H