diff --git a/pkg/smith/lib/configuration.dart b/pkg/smith/lib/configuration.dart
index 370e772a034b..9544b3ab4cc0 100644
--- a/pkg/smith/lib/configuration.dart
+++ b/pkg/smith/lib/configuration.dart
@@ -381,7 +381,12 @@ class Configuration {
         useHotReload = useHotReload ?? false,
         useHotReloadRollback = useHotReloadRollback ?? false,
         useSdk = useSdk ?? false,
-        useQemu = useQemu ?? false;
+        useQemu = useQemu ?? false {
+    if (name.contains(" ")) {
+      throw ArgumentError(
+          "Name of test configuration cannot contain spaces: $name");
+    }
+  }
 
   /// Returns `true` if this configuration's options all have the same values
   /// as [other].
diff --git a/pkg/smith/test/configuration_test.dart b/pkg/smith/test/configuration_test.dart
index d558cc2bc481..7a5b4244228a 100644
--- a/pkg/smith/test/configuration_test.dart
+++ b/pkg/smith/test/configuration_test.dart
@@ -303,7 +303,7 @@ void main() {
       );
 
       var debugWithAsserts2 = Configuration(
-        "different name",
+        "different-name",
         Architecture.x64,
         Compiler.dart2js,
         Mode.debug,
diff --git a/pkg/test_runner/lib/src/options.dart b/pkg/test_runner/lib/src/options.dart
index 7c51016f1095..af07581ab9b7 100644
--- a/pkg/test_runner/lib/src/options.dart
+++ b/pkg/test_runner/lib/src/options.dart
@@ -854,7 +854,7 @@ compiler.''',
             for (var sanitizerName in sanitizers.split(",")) {
               var sanitizer = Sanitizer.find(sanitizerName);
               var configuration = Configuration(
-                  "custom configuration_${configurationNumber++}",
+                  "custom-configuration-${configurationNumber++}",
                   architecture,
                   compiler,
                   mode,