diff --git a/src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintSettingRule.java b/src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintSettingRule.java
index fe47d8f..7449ece 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintSettingRule.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintSettingRule.java
@@ -43,7 +43,9 @@
         constraint list (such as for a <code>config_setting</code>) that requires a particular value
         for that setting.
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
-        .add(attr(DEFAULT_CONSTRAINT_VALUE_ATTR, BuildType.NODEP_LABEL))
+        .add(
+            attr(DEFAULT_CONSTRAINT_VALUE_ATTR, BuildType.NODEP_LABEL)
+                .nonconfigurable("constants must be consistent across configurations"))
         .build();
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintValueRule.java b/src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintValueRule.java
index 1a34bff..b716a0a 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintValueRule.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/platform/ConstraintValueRule.java
@@ -42,7 +42,8 @@
                 .mandatory()
                 .allowedRuleClasses(ConstraintSettingRule.RULE_NAME)
                 .allowedFileTypes(FileTypeSet.NO_FILE)
-                .mandatoryProviders(ConstraintSettingInfo.PROVIDER.id()))
+                .mandatoryProviders(ConstraintSettingInfo.PROVIDER.id())
+                .nonconfigurable("constants must be consistent across configurations"))
         .build();
   }