diff --git a/src/glsl/ast_function.cpp b/src/glsl/ast_function.cpp
index 918be6966d5..36a0d193d9e 100644
--- a/src/glsl/ast_function.cpp
+++ b/src/glsl/ast_function.cpp
@@ -1791,7 +1791,7 @@ ast_function_expression::hir(exec_list *instructions,
       return value;
    }
 
-   return ir_rvalue::error_value(ctx);
+   unreachable("not reached");
 }
 
 ir_rvalue *