diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java b/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
index df50202..6043cda 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BuildView.java
@@ -60,6 +60,7 @@
 import com.google.devtools.build.lib.packages.PackageSpecification;
 import com.google.devtools.build.lib.packages.RawAttributeMapper;
 import com.google.devtools.build.lib.packages.Rule;
+import com.google.devtools.build.lib.packages.RuleTransitionFactory;
 import com.google.devtools.build.lib.packages.Target;
 import com.google.devtools.build.lib.packages.TargetUtils;
 import com.google.devtools.build.lib.pkgcache.LoadingResult;
@@ -855,11 +856,12 @@
 
       Attribute.Transition ruleclassTransition = null;
       if (targetAndConfig.getTarget().getAssociatedRule() != null) {
-        ruleclassTransition = targetAndConfig
-            .getTarget()
-            .getAssociatedRule()
-            .getRuleClassObject()
-            .getTransition();
+        Rule associatedRule = targetAndConfig.getTarget().getAssociatedRule();
+        RuleTransitionFactory transitionFactory =
+            associatedRule.getRuleClassObject().getTransitionFactory();
+        if (transitionFactory != null) {
+          ruleclassTransition = transitionFactory.buildTransitionFor(associatedRule);
+        }
       }
       if (targetAndConfig.getConfiguration() != null) {
         asDeps.put(targetAndConfig.getConfiguration(),
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfiguration.java b/src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfiguration.java
index e7df822..1fc05d8 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/config/BuildConfiguration.java
@@ -56,6 +56,7 @@
 import com.google.devtools.build.lib.packages.Rule;
 import com.google.devtools.build.lib.packages.RuleClass;
 import com.google.devtools.build.lib.packages.RuleClassProvider;
+import com.google.devtools.build.lib.packages.RuleTransitionFactory;
 import com.google.devtools.build.lib.packages.Target;
 import com.google.devtools.build.lib.rules.test.TestActionBuilder;
 import com.google.devtools.build.lib.skylarkinterface.SkylarkCallable;
@@ -1849,15 +1850,18 @@
       transitionsManager.configurationHook(fromRule, attribute, toTarget, this);
 
       Rule associatedRule = toTarget.getAssociatedRule();
-      PatchTransition ruleClassTransition = (PatchTransition)
-          associatedRule.getRuleClassObject().getTransition();
-
-      if (ruleClassTransition != null) {
-        if (currentTransition == ConfigurationTransition.NONE) {
-          currentTransition = ruleClassTransition;
-        } else {
-          currentTransition = new ComposingSplitTransition(ruleClassTransition,
-              currentTransition);
+      RuleTransitionFactory transitionFactory =
+          associatedRule.getRuleClassObject().getTransitionFactory();
+      if (transitionFactory != null) {
+        PatchTransition ruleClassTransition = (PatchTransition)
+            transitionFactory.buildTransitionFor(associatedRule);
+        if (ruleClassTransition != null) {
+          if (currentTransition == ConfigurationTransition.NONE) {
+            currentTransition = ruleClassTransition;
+          } else {
+            currentTransition = new ComposingSplitTransition(ruleClassTransition,
+                currentTransition);
+          }
         }
       }
 
diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
index eeacba5..1a2dbb2 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
@@ -445,6 +445,22 @@
       }
     }
 
+    /**
+     * A RuleTransitionFactory which always returns the same transition.
+     */
+    private static final class FixedTransitionFactory implements RuleTransitionFactory {
+      private final Transition transition;
+
+      private FixedTransitionFactory(Transition transition) {
+        this.transition = transition;
+      }
+
+      @Override
+      public Transition buildTransitionFor(Rule rule) {
+        return transition;
+      }
+    }
+
     /** List of required attributes for normal rules, name and type. */
     public static final ImmutableList<Attribute> REQUIRED_ATTRIBUTES_FOR_NORMAL_RULES =
         ImmutableList.of(attr("tags", Type.STRING_LIST).build());
@@ -470,7 +486,7 @@
     private boolean outputsDefaultExecutable = false;
     private ImplicitOutputsFunction implicitOutputsFunction = ImplicitOutputsFunction.NONE;
     private Configurator<?, ?> configurator = NO_CHANGE;
-    private Transition transition;
+    private RuleTransitionFactory transitionFactory;
     private ConfiguredTargetFactory<?, ?> configuredTargetFactory = null;
     private PredicateWithMessage<Rule> validityPredicate =
         PredicatesWithMessage.<Rule>alwaysTrue();
@@ -584,7 +600,7 @@
           outputsDefaultExecutable,
           implicitOutputsFunction,
           configurator,
-          transition,
+          transitionFactory,
           configuredTargetFactory,
           validityPredicate,
           preferredDependencyPredicate,
@@ -718,8 +734,9 @@
     public Builder cfg(Configurator<?, ?> configurator) {
       Preconditions.checkState(type != RuleClassType.ABSTRACT,
           "Setting not inherited property (cfg) of abstract rule class '%s'", name);
-      Preconditions.checkState(transition == null,
-          "Property cfg cannot be set to both a configurator and a transition");
+      Preconditions.checkState(this.transitionFactory == null && this.configurator == NO_CHANGE,
+          "Property cfg has already been set");
+      Preconditions.checkNotNull(configurator);
       this.configurator = configurator;
       return this;
     }
@@ -734,9 +751,20 @@
     public Builder cfg(Transition transition) {
       Preconditions.checkState(type != RuleClassType.ABSTRACT,
           "Setting not inherited property (cfg) of abstract rule class '%s'", name);
-      Preconditions.checkState(configurator == NO_CHANGE,
-          "Property cfg cannot be set to both a configurator and a transition");
-      this.transition = transition;
+      Preconditions.checkState(this.transitionFactory == null && this.configurator == NO_CHANGE,
+          "Property cfg has already been set");
+      Preconditions.checkNotNull(transition);
+      this.transitionFactory = new FixedTransitionFactory(transition);
+      return this;
+    }
+
+    public Builder cfg(RuleTransitionFactory transitionFactory) {
+      Preconditions.checkState(type != RuleClassType.ABSTRACT,
+          "Setting not inherited property (cfg) of abstract rule class '%s'", name);
+      Preconditions.checkState(this.transitionFactory == null && this.configurator == NO_CHANGE,
+          "Property cfg has already been set");
+      Preconditions.checkNotNull(transitionFactory);
+      this.transitionFactory = transitionFactory;
       return this;
     }
 
@@ -1000,12 +1028,10 @@
   private final Configurator<?, ?> configurator;
 
   /**
-   * A configuration transition that should be applied on any edge of the configured target graph
-   * that leads into a target of this rule class.
-   *
-   * <p>This transition must be a PatchTransition, but that class is not accessible in this package.
+   * A factory which will produce a configuration transition that should be applied on any edge of
+   * the configured target graph that leads into a target of this rule class.
    */
-  private final Transition transition;
+  private final RuleTransitionFactory transitionFactory;
 
   /**
    * The factory that creates configured targets from this rule.
@@ -1090,7 +1116,7 @@
       boolean outputsDefaultExecutable,
       ImplicitOutputsFunction implicitOutputsFunction,
       Configurator<?, ?> configurator,
-      Transition transition,
+      RuleTransitionFactory transitionFactory,
       ConfiguredTargetFactory<?, ?> configuredTargetFactory,
       PredicateWithMessage<Rule> validityPredicate,
       Predicate<String> preferredDependencyPredicate,
@@ -1112,7 +1138,7 @@
     this.binaryOutput = binaryOutput;
     this.implicitOutputsFunction = implicitOutputsFunction;
     this.configurator = Preconditions.checkNotNull(configurator);
-    this.transition = transition;
+    this.transitionFactory = transitionFactory;
     this.configuredTargetFactory = configuredTargetFactory;
     this.validityPredicate = validityPredicate;
     this.preferredDependencyPredicate = preferredDependencyPredicate;
@@ -1182,8 +1208,8 @@
     return (Configurator<C, R>) configurator;
   }
 
-  public Transition getTransition() {
-    return transition;
+  public RuleTransitionFactory getTransitionFactory() {
+    return transitionFactory;
   }
 
   @SuppressWarnings("unchecked")
diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleTransitionFactory.java b/src/main/java/com/google/devtools/build/lib/packages/RuleTransitionFactory.java
new file mode 100644
index 0000000..215461f
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleTransitionFactory.java
@@ -0,0 +1,32 @@
+// Copyright 2017 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.devtools.build.lib.packages;
+
+import com.google.devtools.build.lib.packages.Attribute.Transition;
+import javax.annotation.Nullable;
+
+/**
+ * Customizable transition which accepts the rule's nonconfigurable attributes.
+ */
+public interface RuleTransitionFactory {
+  /**
+   * Generates a transition to be used when entering the given rule.
+   *
+   * <p>This transition must be a PatchTransition, but that class is not accessible in this package.
+   * If this class determines that no transition should be performed, it should return {@code null}.
+   */
+  @Nullable
+  Transition buildTransitionFor(Rule rule);
+}