diff --git a/tests/utils.py b/tests/utils.py
index 4e9ac9f0..2937a2f1 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -23,7 +23,7 @@
 
 # Unit for timeouts. May be increased on slow machines by setting the
 # WEBSOCKETS_TESTS_TIMEOUT_FACTOR environment variable.
-MS = 0.001 * int(os.environ.get("WEBSOCKETS_TESTS_TIMEOUT_FACTOR", "1"))
+MS = 0.001 * float(os.environ.get("WEBSOCKETS_TESTS_TIMEOUT_FACTOR", "1"))
 
 # PyPy has a performance penalty for this test suite.
 if platform.python_implementation() == "PyPy":  # pragma: no cover