diff --git a/adafruit_pioasm.py b/adafruit_pioasm.py
index e225a7d..3bae992 100644
--- a/adafruit_pioasm.py
+++ b/adafruit_pioasm.py
@@ -170,7 +170,7 @@ def assemble(text_program):
                 raise RuntimeError("Set value out of range")
             assembled[-1] |= value
         else:
-            raise RuntimeError("Unknown instruction:" + instruction)
+            raise RuntimeError("Unknown instruction:" + instruction[0])
         assembled[-1] |= delay << 8
     # print(hex(assembled[-1]))