diff --git a/src/lisp/s-expr.pla b/src/lisp/s-expr.pla
index f4c929f..d52fc53 100644
--- a/src/lisp/s-expr.pla
+++ b/src/lisp/s-expr.pla
@@ -908,6 +908,11 @@ export def eval_expr(expr)#1
       else
         curl = NULL // Set-up for in-line LAMBDA
       fin
+      if !expr_car // Make sure we don't hang
+        puts("Invalid function:"); print_expr(expr); putln
+        expr = NULL
+        break
+      fin
       if expr_car->type == CONS_TYPE
         if expr_car=>car == sym_funarg // FUNARG
           expr = eval_funarg(expr_car, expr=>cdr)
@@ -919,6 +924,10 @@ export def eval_expr(expr)#1
         fin
         if expr_car=>car == sym_lambda // LAMBDA
           curl, expr = apply_args(curl, expr_car, expr=>cdr)
+        else
+          puts("LAMBDA expected:"); print_expr(expr); putln
+          expr = NULL
+          break
         fin
       fin
     else