diff --git a/src/function.cpp b/src/function.cpp
index f65d3414d..59fa9b8cb 100644
--- a/src/function.cpp
+++ b/src/function.cpp
@@ -184,6 +184,7 @@ std::shared_ptr<const function_properties_t> function_get_properties(const wcstr
 
 int function_exists(const wcstring &cmd, parser_t &parser) {
     ASSERT_IS_MAIN_THREAD();
+    if (!valid_func_name(cmd)) return false;
     if (parser_keywords_is_reserved(cmd)) return 0;
     try_autoload(cmd, parser);
     auto funcset = function_set.acquire();
@@ -197,8 +198,9 @@ void function_load(const wcstring &cmd, parser_t &parser) {
     }
 }
 
-int function_exists_no_autoload(const wcstring &cmd) {
-    if (parser_keywords_is_reserved(cmd)) return 0;
+bool function_exists_no_autoload(const wcstring &cmd) {
+    if (!valid_func_name(cmd)) return false;
+    if (parser_keywords_is_reserved(cmd)) return false;
     auto funcset = function_set.acquire();
 
     // Check if we either have the function, or it could be autoloaded.
diff --git a/src/function.h b/src/function.h
index e7e477cbd..8af4d8649 100644
--- a/src/function.h
+++ b/src/function.h
@@ -72,7 +72,7 @@ int function_exists(const wcstring &cmd, parser_t &parser);
 void function_load(const wcstring &cmd, parser_t &parser);
 
 /// Returns true if the function with the name name exists, without triggering autoload.
-int function_exists_no_autoload(const wcstring &cmd);
+bool function_exists_no_autoload(const wcstring &cmd);
 
 /// Returns all function names.
 ///