diff --git a/adafruit_pioasm.py b/adafruit_pioasm.py
index 514d1ba..fa5a529 100644
--- a/adafruit_pioasm.py
+++ b/adafruit_pioasm.py
@@ -94,14 +94,14 @@ def __init__(self, text_program: str, *, build_debuginfo: bool = False) -> None:
         for line in instructions:
             instruction = splitter(line.strip())
             delay = 0
-            if instruction[-1].endswith("]"):  # Delay
+            if len(instruction) > 1 and instruction[-1].endswith("]"):  # Delay
                 delay = int(instruction[-1].strip("[]"), 0)
                 if delay < 0:
                     raise RuntimeError("Delay negative:", delay)
                 if delay > max_delay:
                     raise RuntimeError("Delay too long:", delay)
                 instruction.pop()
-            if len(instruction) > 1 and instruction[-2] == "side":
+            if len(instruction) > 2 and instruction[-2] == "side":
                 if sideset_count == 0:
                     raise RuntimeError("No side_set count set")
                 sideset_value = int(instruction[-1], 0)
@@ -236,7 +236,7 @@ def __init__(self, text_program: str, *, build_debuginfo: bool = False) -> None:
                     raise RuntimeError("Set value out of range")
                 assembled[-1] |= value
             else:
-                raise RuntimeError("Unknown instruction:" + instruction[0])
+                raise RuntimeError(f"Unknown instruction: {instruction[0]}")
             assembled[-1] |= delay << 8
             # print(bin(assembled[-1]))
 
diff --git a/tests/test_misc.py b/tests/test_misc.py
new file mode 100644
index 0000000..ea07e51
--- /dev/null
+++ b/tests/test_misc.py
@@ -0,0 +1,39 @@
+# SPDX-FileCopyrightText: KB Sriram
+#
+# SPDX-License-Identifier: MIT
+
+"""
+Tests out
+"""
+
+from pytest_helpers import assert_assembly_fails
+
+
+def test_invalid_sideset() -> None:
+    source = [
+        ".side_set 2",
+        "side 2 [5]",
+    ]
+    assert_assembly_fails(
+        "\n".join(source), match="Unknown instruction: side", errtype=RuntimeError
+    )
+
+    source = [
+        ".side_set 2",
+        "side 2",
+    ]
+    assert_assembly_fails(
+        "\n".join(source), match="Unknown instruction: side", errtype=RuntimeError
+    )
+
+
+def test_invalid_delay() -> None:
+    assert_assembly_fails(
+        "[5]", match=r"Unknown instruction: \[5\]", errtype=RuntimeError
+    )
+
+
+def test_invalid_instruction() -> None:
+    assert_assembly_fails(
+        "bad", match=r"Unknown instruction: bad", errtype=RuntimeError
+    )