diff --git a/src/compiler/glsl/ast_function.cpp b/src/compiler/glsl/ast_function.cpp
index ac3b52d..fb50e27 100644
--- a/src/compiler/glsl/ast_function.cpp
+++ b/src/compiler/glsl/ast_function.cpp
@@ -2099,13 +2099,20 @@ ast_function_expression::hir(exec_list *instructions,
       process_parameters(instructions, &actual_parameters, &this->expressions,
                          state);
 
-      if (id->oper == ast_array_index) {
+      switch (id->oper) {
+      case ast_array_index:
          array_idx = generate_array_index(ctx, instructions, state, loc,
                                           id->subexpressions[0],
                                           id->subexpressions[1], &func_name,
                                           &actual_parameters);
-      } else {
+         break;
+      case ast_int_constant:
+         _mesa_glsl_error(& loc, state, "%i is no valid function name",
+                          id->primary_expression.identifier);
+         return ir_rvalue::error_value(ctx);
+      default:
          func_name = id->primary_expression.identifier;
+         break;
       }
 
       /* an error was emitted earlier */