diff --git a/pmd/regress/test/net/sourceforge/pmd/rules/SimplifyConditionalTest.java b/pmd/regress/test/net/sourceforge/pmd/rules/SimplifyConditionalTest.java
index a224a9c6e4..6d5e1f2b6e 100644
--- a/pmd/regress/test/net/sourceforge/pmd/rules/SimplifyConditionalTest.java
+++ b/pmd/regress/test/net/sourceforge/pmd/rules/SimplifyConditionalTest.java
@@ -20,6 +20,7 @@ public class SimplifyConditionalTest extends SimpleAggregatorTst {
             new TestDescriptor(TEST3, "transpose x and null, still bad", 1, rule),
             new TestDescriptor(TEST4, "conditional or and !(instanceof)", 1, rule),
             new TestDescriptor(TEST5, "indexing into array is ok", 0, rule),
+            new TestDescriptor(TEST6, "test for null on unrelated object is ok", 0, rule),
         });
     }
 
@@ -58,4 +59,11 @@ public class SimplifyConditionalTest extends SimpleAggregatorTst {
             " }" + PMD.EOL +
             "}";
 
+    private static final String TEST6 =
+            "public class Foo {" + PMD.EOL +
+            " void bar(Object x) {" + PMD.EOL +
+            "  if (x instanceof String && ((String)x).substring(2) != null) {}" + PMD.EOL +
+            " }" + PMD.EOL +
+            "}";
+
 }
diff --git a/pmd/rulesets/design.xml b/pmd/rulesets/design.xml
index b01d8d8fca..1152d6958d 100644
--- a/pmd/rulesets/design.xml
+++ b/pmd/rulesets/design.xml
@@ -1020,7 +1020,7 @@ No need to check for null before an instanceof; the instanceof keyword returns f
   UnaryExpressionNotPlusMinus
    [@Image='!']//InstanceOfExpression[PrimaryExpression
      //Name/@Image = ancestor::ConditionalOrExpression/EqualityExpression
-      //PrimaryPrefix/Name/@Image]]
+      /PrimaryExpression/PrimaryPrefix/Name/@Image]]
 or
 ConditionalAndExpression
  [EqualityExpression[@Image='!=']//NullLiteral
@@ -1028,7 +1028,7 @@ ConditionalAndExpression
 InstanceOfExpression
  [PrimaryExpression[count(PrimarySuffix[@ArrayDereference='true'])=0]
   //Name/@Image = ancestor::ConditionalAndExpression
-   /EqualityExpression//PrimaryPrefix/Name/@Image]]]
+   /EqualityExpression/PrimaryExpression/PrimaryPrefix/Name/@Image]]]
  ]]>
                   </value>
               </property>