diff --git a/src/scancode/interrupt.py b/src/scancode/interrupt.py
index e26d090567..1a21306cce 100644
--- a/src/scancode/interrupt.py
+++ b/src/scancode/interrupt.py
@@ -86,9 +86,20 @@ def handler(signum, frame):
             raise TimeoutError
 
         try:
-            create_signal(SIGALRM, handler)
-            setitimer(ITIMER_REAL, timeout)
-            return NO_ERROR, func(*(args or ()), **(kwargs or {}))
+    create_signal(SIGALRM, handler)
+    setitimer(ITIMER_REAL, timeout)
+except (ValueError, TypeError):
+    # Signals only work in the main thread.
+    # If we cannot install them, continue without interrupt support.
+    return NO_ERROR, func(*(args or ()), **(kwargs or {}))
+
+    try:
+        return NO_ERROR, func(*(args or ()), **(kwargs or {}))
+    except TimeoutError:
+        return TIMEOUT_MSG % locals(), NO_VALUE
+    except Exception:
+        return ERROR_MSG + traceback_format_exc(), NO_VALUE
+
 
         except TimeoutError:
             return TIMEOUT_MSG % locals(), NO_VALUE
@@ -167,7 +178,10 @@ def async_raise(tid, exctype=Exception):
         from http://tomerfiliba.com/recipes/Thread2/
         license: public domain.
         """
-        assert isinstance(tid, int), 'Invalid  thread id: must an integer'
+        if not isinstance(tid, int):
+            raise TypeError(
+                f"Invalid thread id: must be an integer, got {type(tid).__name__}"
+            )
 
         tid = c_long(tid)
         exception = py_object(Exception)