diff --git a/dev/core/src/com/google/gwt/dev/jjs/impl/JsInteropRestrictionChecker.java b/dev/core/src/com/google/gwt/dev/jjs/impl/JsInteropRestrictionChecker.java
index 93417bd..b8bb599 100644
--- a/dev/core/src/com/google/gwt/dev/jjs/impl/JsInteropRestrictionChecker.java
+++ b/dev/core/src/com/google/gwt/dev/jjs/impl/JsInteropRestrictionChecker.java
@@ -42,6 +42,7 @@
 import com.google.gwt.dev.jjs.ast.JProgram;
 import com.google.gwt.dev.jjs.ast.JReferenceType;
 import com.google.gwt.dev.jjs.ast.JStatement;
+import com.google.gwt.dev.jjs.ast.JType;
 import com.google.gwt.dev.jjs.ast.JVisitor;
 import com.google.gwt.dev.jjs.ast.js.JsniMethodBody;
 import com.google.gwt.dev.js.JsUtils;
@@ -644,13 +645,22 @@
   private void checkJsPropertyConsistency(JMember member, JsMember newMember) {
     if (newMember.setter != null && newMember.getter != null) {
       List<JParameter> setterParams = ((JMethod) newMember.setter).getParams();
-      if (newMember.getter.getType() != setterParams.get(0).getType()) {
+      if (isSameType(newMember.getter.getType(), setterParams.get(0).getType())) {
         logError(member, "JsProperty setter %s and getter %s cannot have inconsistent types.",
             getMemberDescription(newMember.setter), getMemberDescription(newMember.getter));
       }
     }
   }
 
+  /**
+   * Returns true if {@code thisType} is the same type as {@code thatType}.
+   */
+  private boolean isSameType(JType thisType, JType thatType) {
+    // NOTE: The comparison here is made by signature instead of reference equality because under
+    // incremental compilation this types might be reference only and hence not unique.
+    return !thisType.getJavahSignatureName().equals(thatType.getJavahSignatureName());
+  }
+
   private void checkNameConsistency(JMember member) {
     if (member instanceof JMethod) {
       String jsName = member.getJsName();
diff --git a/dev/core/test/com/google/gwt/dev/CompilerTest.java b/dev/core/test/com/google/gwt/dev/CompilerTest.java
index 196e568..1e56f38 100644
--- a/dev/core/test/com/google/gwt/dev/CompilerTest.java
+++ b/dev/core/test/com/google/gwt/dev/CompilerTest.java
@@ -1495,6 +1495,67 @@
     checkIncrementalRecompile_dateStampChange(JsOutputOption.DETAILED);
   }
 
+  // Repro for bug #9518
+  public void testIncrementalRecompile_jsPropertyConsistencyCheck()
+      throws UnableToCompleteException,
+      IOException, InterruptedException {
+    // Supertype defines the getter.
+    MockJavaResource superType =
+        JavaResourceBase.createMockJavaResource(
+            "com.foo.SuperType",
+            "package com.foo;",
+            "import jsinterop.annotations.JsProperty;",
+            "public class SuperType {",
+            "  @JsProperty String getString() { return null; }",
+            "}");
+
+    // Subtype defines the setter.
+    MockJavaResource subType =
+        JavaResourceBase.createMockJavaResource(
+            "com.foo.SubType",
+            "package com.foo;",
+            "import jsinterop.annotations.JsProperty;",
+            "public class SubType extends SuperType {",
+            "  @JsProperty void setString(String s) {}",
+            "}");
+
+    MockJavaResource testEntryPoint =
+        JavaResourceBase.createMockJavaResource(
+            "com.foo.TestEntryPoint",
+            "package com.foo;",
+            "import com.google.gwt.core.client.EntryPoint;",
+            "public class TestEntryPoint implements EntryPoint {",
+            "  public void onModuleLoad() {",
+            // Create Impl and pass it to JS but do not explicitly call m
+            "    new SubType();",
+            "  }",
+            "}");
+
+    MockResource moduleResource =
+        JavaResourceBase.createMockResource(
+            "com/foo/TestModule.gwt.xml",
+            "<module>",
+            "  <source path=''/>",
+            "  <entry-point class='com.foo.TestEntryPoint'/>",
+            "</module>");
+
+    MinimalRebuildCache relinkMinimalRebuildCache = new MinimalRebuildCache();
+    File relinkApplicationDir = Files.createTempDir();
+
+    // Perform a first compile.
+    compileToJs(relinkApplicationDir, "com.foo.TestModule",
+        Lists.newArrayList(moduleResource, testEntryPoint, subType, superType),
+        relinkMinimalRebuildCache, null, JsOutputOption.OBFUSCATED);
+
+    // Invalidate ONLY the subtype. The types referred by the parameters of supertype methods are
+    // going to be reference only which means that the supertype property will have a reference
+    // to a JClassType for "java.lang.String" that isExternal() and is different from the
+    // (non external) reference in the supertype.
+    relinkMinimalRebuildCache.markSourceFileStale("com/foo/SubType.java");
+    compileToJs(relinkApplicationDir, "com.foo.TestModule", Lists.<MockResource> newArrayList(),
+        relinkMinimalRebuildCache, null, JsOutputOption.OBFUSCATED);
+  }
+
   public void testIncrementalRecompile_invalidatePreamble() throws UnableToCompleteException,
       IOException, InterruptedException {
     MinimalRebuildCache relinkMinimalRebuildCache = new MinimalRebuildCache();