diff --git a/cibuildwheel/__main__.py b/cibuildwheel/__main__.py
index 6252b4f2..bdc76287 100644
--- a/cibuildwheel/__main__.py
+++ b/cibuildwheel/__main__.py
@@ -177,10 +177,11 @@ def detect_warnings(platform, build_options):
 
     # warn about deprecated {python} and {pip}
     for option_name in ['test_command', 'before_build']:
-        option_value = build_options.get(option_name, '')
+        option_value = build_options.get(option_name)
 
-        if '{python}' in option_value or '{pip}' in option_value:
-            warnings.append(option_name + ": '{python}' and '{pip}' are no longer needed, and will be removed in a future release. Simply use 'python' or 'pip' instead.")
+        if option_value:
+            if '{python}' in option_value or '{pip}' in option_value:
+                warnings.append(option_name + ": '{python}' and '{pip}' are no longer needed, and will be removed in a future release. Simply use 'python' or 'pip' instead.")
 
     return warnings