diff --git a/src/com/google/javascript/jscomp/DeadPropertyAssignmentElimination.java b/src/com/google/javascript/jscomp/DeadPropertyAssignmentElimination.java
index f95d02aa83d..d389e5a6ca2 100644
--- a/src/com/google/javascript/jscomp/DeadPropertyAssignmentElimination.java
+++ b/src/com/google/javascript/jscomp/DeadPropertyAssignmentElimination.java
@@ -20,6 +20,7 @@
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Iterators;
 import com.google.common.collect.PeekingIterator;
+import com.google.common.collect.Sets;
 import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
 import com.google.javascript.jscomp.NodeTraversal.Callback;
 import com.google.javascript.rhino.Node;
@@ -48,6 +49,7 @@
  * <li>Any reference to a property getter/setter is treated like a call that escapes all props.</li>
  * <li>If there's an Object.definePropert{y,ies} call where the object or property name is aliased
  * then the optimization does not run at all.</li>
+ * <li>Properties names defined in externs will not be pruned.</li>
  * </ul>
  */
 public class DeadPropertyAssignmentElimination implements CompilerPass {
@@ -65,6 +67,12 @@ public class DeadPropertyAssignmentElimination implements CompilerPass {
 
   @Override
   public void process(Node externs, Node root) {
+    // GatherExternProperties must be enabled for this pass to safely know what property writes are
+    // eligible for removal.
+    if (compiler.getExternProperties() == null) {
+      return;
+    }
+
     GetterSetterCollector getterSetterCollector = new GetterSetterCollector();
     NodeTraversal.traverseEs6(compiler, root, getterSetterCollector);
 
@@ -73,8 +81,9 @@ public void process(Node externs, Node root) {
       return;
     }
 
-    NodeTraversal.traverseEs6(compiler, root,
-        new FunctionVisitor(compiler, getterSetterCollector.propNames));
+    Set<String> blacklistedPropNames = Sets.union(
+        getterSetterCollector.propNames, compiler.getExternProperties());
+    NodeTraversal.traverseEs6(compiler, root, new FunctionVisitor(compiler, blacklistedPropNames));
   }
 
   private static class FunctionVisitor extends AbstractPostOrderCallback {
@@ -82,14 +91,13 @@ private static class FunctionVisitor extends AbstractPostOrderCallback {
     private final AbstractCompiler compiler;
 
     /**
-     * A set of properties names that are known to be assigned to getter/setters. This is important
-     * since any reference to these properties needs to be treated as if it were a call.
+     * A set of properties names that are potentially unsafe to remove duplicate writes to.
      */
-    private final Set<String> getterSetterNames;
+    private final Set<String> blacklistedPropNames;
 
-    FunctionVisitor(AbstractCompiler compiler, Set<String> getterSetterNames) {
+    FunctionVisitor(AbstractCompiler compiler, Set<String> blacklistedPropNames) {
       this.compiler = compiler;
-      this.getterSetterNames = getterSetterNames;
+      this.blacklistedPropNames = blacklistedPropNames;
     }
 
     @Override
@@ -104,7 +112,7 @@ public void visit(NodeTraversal t, Node n, Node parent) {
       }
 
       FindCandidateAssignmentTraversal traversal =
-          new FindCandidateAssignmentTraversal(getterSetterNames, NodeUtil.isConstructor(n));
+          new FindCandidateAssignmentTraversal(blacklistedPropNames, NodeUtil.isConstructor(n));
       NodeTraversal.traverseEs6(compiler, body, traversal);
 
       // Any candidate property assignment can have a write removed if that write is never read
@@ -221,18 +229,17 @@ private static class FindCandidateAssignmentTraversal implements Callback {
     Map<String, Property> propertyMap = new HashMap<>();
 
     /**
-     * A set of properties names that are known to be assigned to getter/setters. This is important
-     * since any reference to these properties needs to be treated as if it were a call.
+     * A set of properties names that are potentially unsafe to remove duplicate writes to.
      */
-    private final Set<String> getterSetterNames;
+    private final Set<String> blacklistedPropNames;
 
     /**
      * Whether or not the function being analyzed is a constructor.
      */
     private final boolean isConstructor;
 
-    FindCandidateAssignmentTraversal(Set<String> getterSetterNames, boolean isConstructor) {
-      this.getterSetterNames = getterSetterNames;
+    FindCandidateAssignmentTraversal(Set<String> blacklistedPropNames, boolean isConstructor) {
+      this.blacklistedPropNames = blacklistedPropNames;
       this.isConstructor = isConstructor;
     }
 
@@ -361,7 +368,7 @@ private boolean visitNode(Node n, Node parent) {
           // Handle potential getters/setters.
           if (n.isGetProp()
               && n.getLastChild().isString()
-              && getterSetterNames.contains(n.getLastChild().getString())) {
+              && blacklistedPropNames.contains(n.getLastChild().getString())) {
             // We treat getters/setters as if they were a call, thus we mark all properties as read.
             markAllPropsRead();
             return true;
diff --git a/test/com/google/javascript/jscomp/DeadPropertyAssignmentEliminationTest.java b/test/com/google/javascript/jscomp/DeadPropertyAssignmentEliminationTest.java
index 6fe2c51dc91..5f547ef6d48 100644
--- a/test/com/google/javascript/jscomp/DeadPropertyAssignmentEliminationTest.java
+++ b/test/com/google/javascript/jscomp/DeadPropertyAssignmentEliminationTest.java
@@ -22,6 +22,11 @@
 
 public class DeadPropertyAssignmentEliminationTest extends CompilerTestCase {
 
+  @Override
+  public void setUp() throws Exception {
+    enableGatherExternProperties();
+  }
+
   public void testBasic() {
     testSame(LINE_JOINER.join(
         "var foo = function() {",
@@ -988,6 +993,43 @@ public void testObjectDefineProperties_aliasedVars() {
             "}"));
   }
 
+  public void testPropertyDefinedInExterns() {
+    String externs = LINE_JOINER.join(
+        "var window = {};",
+        "/** @type {number} */ window.innerWidth",
+        "/** @constructor */",
+        "var Image = function() {};",
+        "/** @type {string} */ Image.prototype.src;"
+    );
+
+    testSame(
+        externs,
+        LINE_JOINER.join(
+            "function z() {",
+            "  window.innerWidth = 10;",
+            "  window.innerWidth = 20;",
+            "}"),
+        null);
+
+    testSame(
+        externs,
+        LINE_JOINER.join(
+            "function z() {",
+            "  var img = new Image();",
+            "  img.src = '';",
+            "  img.src = 'foo.bar';",
+            "}"),
+        null);
+
+    testSame(
+        externs,
+        LINE_JOINER.join(
+            "function z(x) {",
+            "  x.src = '';",
+            "  x.src = 'foo.bar';",
+            "}"),
+        null);
+  }
 
   @Override
   protected CompilerPass getProcessor(Compiler compiler) {