diff --git a/src/com/google/common/css/JobDescription.java b/src/com/google/common/css/JobDescription.java
index f9c94e2e..08d70571 100644
--- a/src/com/google/common/css/JobDescription.java
+++ b/src/com/google/common/css/JobDescription.java
@@ -48,6 +48,7 @@ public class JobDescription {
   public final boolean eliminateDeadStyles;
   public final boolean allowDefPropagation;
   public final boolean allowUnrecognizedFunctions;
+  public final boolean allowDuplicateDeclarations;
   public final Set<String> allowedNonStandardFunctions;
   public final boolean allowUnrecognizedProperties;
   public final Set<String> allowedUnrecognizedProperties;
@@ -127,6 +128,7 @@ public enum SourceMapDetailLevel { ALL, DEFAULT }
       boolean swapLeftRightInUrl, boolean simplifyCss,
       boolean eliminateDeadStyles, boolean allowDefPropagation,
       boolean allowUnrecognizedFunctions,
+      boolean allowDuplicateDeclarations,
       Set<String> allowedNonStandardFunctions,
       boolean allowUnrecognizedProperties,
       Set<String> allowedUnrecognizedProperties, boolean allowUndefinedConstants,
@@ -167,6 +169,7 @@ public enum SourceMapDetailLevel { ALL, DEFAULT }
     this.eliminateDeadStyles = eliminateDeadStyles;
     this.allowDefPropagation = allowDefPropagation;
     this.allowUnrecognizedFunctions = allowUnrecognizedFunctions;
+    this.allowDuplicateDeclarations = allowDuplicateDeclarations;
     this.allowedNonStandardFunctions = ImmutableSet.copyOf(
         allowedNonStandardFunctions);
     this.allowUnrecognizedProperties = allowUnrecognizedProperties;
diff --git a/src/com/google/common/css/JobDescriptionBuilder.java b/src/com/google/common/css/JobDescriptionBuilder.java
index 0f4a9d5e..62f6774b 100644
--- a/src/com/google/common/css/JobDescriptionBuilder.java
+++ b/src/com/google/common/css/JobDescriptionBuilder.java
@@ -52,6 +52,7 @@ public class JobDescriptionBuilder {
   boolean eliminateDeadStyles;
   boolean allowDefPropagation;
   boolean allowUnrecognizedFunctions;
+  boolean allowDuplicateDeclarations;
   Set<String> allowedNonStandardFunctions;
   boolean allowUnrecognizedProperties;
   Set<String> allowedUnrecognizedProperties;
@@ -91,6 +92,7 @@ public JobDescriptionBuilder() {
     this.eliminateDeadStyles = false;
     this.allowDefPropagation = false;
     this.allowUnrecognizedFunctions = false;
+    this.allowDuplicateDeclarations = false;
     this.allowedNonStandardFunctions = Sets.newHashSet();
     this.allowUnrecognizedProperties = false;
     this.allowedUnrecognizedProperties = Sets.newHashSet();
@@ -129,6 +131,7 @@ public JobDescriptionBuilder copyFrom(JobDescription jobToCopy) {
     this.eliminateDeadStyles = jobToCopy.eliminateDeadStyles;
     this.allowDefPropagation = jobToCopy.allowDefPropagation;
     this.allowUnrecognizedFunctions = jobToCopy.allowUnrecognizedFunctions;
+    this.allowDuplicateDeclarations = jobToCopy.allowDuplicateDeclarations;
     this.allowedNonStandardFunctions =
         ImmutableSet.copyOf(jobToCopy.allowedNonStandardFunctions);
     this.allowUnrecognizedProperties = jobToCopy.allowUnrecognizedProperties;
@@ -341,6 +344,16 @@ public JobDescriptionBuilder setAllowedNonStandardFunctions(
     return this;
   }
 
+  public JobDescriptionBuilder setAllowDuplicateDeclarations(boolean allow) {
+      checkJobIsNotAlreadyCreated();
+      this.allowDuplicateDeclarations = allow;
+      return this;
+  }
+
+  public JobDescriptionBuilder allowDuplicateDeclarations() {
+    return setAllowDuplicateDeclarations(true);
+  }
+
   public JobDescriptionBuilder setAllowUnrecognizedProperties(boolean allow) {
     checkJobIsNotAlreadyCreated();
     this.allowUnrecognizedProperties = allow;
@@ -487,8 +500,9 @@ public JobDescription getJobDescription() {
         copyrightNotice, outputFormat, inputOrientation, outputOrientation,
         optimize, trueConditionNames, useInternalBidiFlipper, swapLtrRtlInUrl,
         swapLeftRightInUrl, simplifyCss, eliminateDeadStyles,
-        allowDefPropagation, allowUnrecognizedFunctions, allowedNonStandardFunctions,
-        allowUnrecognizedProperties, allowedUnrecognizedProperties, allowUndefinedConstants,
+        allowDefPropagation, allowUnrecognizedFunctions, allowDuplicateDeclarations,
+        allowedNonStandardFunctions, allowUnrecognizedProperties,
+        allowedUnrecognizedProperties, allowUndefinedConstants,
         allowMozDocument, vendor,
         allowKeyframes, allowWebkitKeyframes, processDependencies,
         allowedAtRules, cssRenamingPrefix, excludedClassesFromRenaming,
diff --git a/src/com/google/common/css/compiler/commandline/ClosureCommandLineCompiler.java b/src/com/google/common/css/compiler/commandline/ClosureCommandLineCompiler.java
index c33996e8..6c93e52f 100644
--- a/src/com/google/common/css/compiler/commandline/ClosureCommandLineCompiler.java
+++ b/src/com/google/common/css/compiler/commandline/ClosureCommandLineCompiler.java
@@ -162,6 +162,10 @@ static class Flags {
         "Allow unrecognized functions.")
     private boolean allowUnrecognizedFunctions = false;
 
+    @Option(name = "--allow-duplicate-declarations", usage =
+        "Allow duplicate declarations.")
+    private boolean allowDuplicateDeclarations = false;
+
     @Option(name = "--allowed-non-standard-function", usage =
         "Specify a non-standard function to whitelist, like alpha()")
     private List<String> allowedNonStandardFunctions = Lists.newArrayList();
@@ -237,6 +241,7 @@ JobDescription createJobDescription() {
       builder.setTrueConditionNames(trueConditions);
       builder.setAllowDefPropagation(allowDefPropagation);
       builder.setAllowUnrecognizedFunctions(allowUnrecognizedFunctions);
+      builder.setAllowDuplicateDeclarations(allowDuplicateDeclarations);
       builder.setAllowedNonStandardFunctions(allowedNonStandardFunctions);
       builder.setAllowedUnrecognizedProperties(allowedUnrecognizedProperties);
       builder.setAllowUnrecognizedProperties(allowUnrecognizedProperties);
diff --git a/src/com/google/common/css/compiler/passes/PassRunner.java b/src/com/google/common/css/compiler/passes/PassRunner.java
index 61557648..54a68885 100644
--- a/src/com/google/common/css/compiler/passes/PassRunner.java
+++ b/src/com/google/common/css/compiler/passes/PassRunner.java
@@ -142,10 +142,12 @@ public void runPasses(CssTree cssTree) {
       new AbbreviatePositionalValues(
           cssTree.getMutatingVisitController()).runPass();
     }
-    if (job.eliminateDeadStyles) {
-      // Report errors for duplicate declarations
+    // Report errors for duplicate declarations
+    if (!job.allowDuplicateDeclarations) {
       new DisallowDuplicateDeclarations(
           cssTree.getVisitController(), errorManager).runPass();
+    }
+    if (job.eliminateDeadStyles) {
       // Split rules by selector and declaration.
       new SplitRulesetNodes(cssTree.getMutatingVisitController()).runPass();
       // Dead code elimination.
diff --git a/tests/com/google/common/css/compiler/commandline/ClosureCommandLineCompilerTest.java b/tests/com/google/common/css/compiler/commandline/ClosureCommandLineCompilerTest.java
index a81a9ae7..f53b7519 100644
--- a/tests/com/google/common/css/compiler/commandline/ClosureCommandLineCompilerTest.java
+++ b/tests/com/google/common/css/compiler/commandline/ClosureCommandLineCompilerTest.java
@@ -76,6 +76,15 @@ public void testAllowDefPropagationDefaultsToTrue() throws Exception {
 
   @Test
 
+  public void testAllowDuplicateDeclarationsDefaultsToFalse() throws Exception {
+    ClosureCommandLineCompiler.Flags flags =
+            ClosureCommandLineCompiler.parseArgs(new String[] {"/dev/null"}, EXIT_CODE_HANDLER);
+    JobDescription jobDescription = flags.createJobDescription();
+    assertThat(jobDescription.allowDuplicateDeclarations).isFalse();
+  }
+
+  @Test
+
   public void testEmptyImportBlocks() throws Exception {
     // See b/29995881
     ErrorManager errorManager = new NewFunctionalTestBase.TestErrorManager(new String[0]);