diff --git a/src/components/ProgramLoader/Assembly.tsx b/src/components/ProgramLoader/Assembly.tsx
index f701a5e0..0166f1f4 100644
--- a/src/components/ProgramLoader/Assembly.tsx
+++ b/src/components/ProgramLoader/Assembly.tsx
@@ -62,6 +62,8 @@ function assemblyFromInputProgram(initialState: InitialState, program: number[])
       l = l.replace(/^(.*)\/\/.*/, "$1");
       // fix unary minus
       l = l.replace(/= -/, "= 0 -");
+      // replace `invalid` instructions with a comment
+      l = l.replace("invalid", "// invalid");
       return l;
     });