diff --git a/WHATSNEW b/WHATSNEW
index 17fbc3509..e235acdc0 100644
--- a/WHATSNEW
+++ b/WHATSNEW
@@ -136,6 +136,9 @@ Fixed bugs:
 * <junit> supports collecting and rerunning failed test cases
   (textXXX methods). Bugzilla 42984.  
 
+* War task failed with "No WEB-INF/web.xml file was added" when called
+  a second time. Bugzilla 43121.
+
 Other changes:
 --------------
 * <script> now has basic support for JavaFX scripts
diff --git a/src/main/org/apache/tools/ant/taskdefs/War.java b/src/main/org/apache/tools/ant/taskdefs/War.java
index f80fec3cf..9940a443f 100644
--- a/src/main/org/apache/tools/ant/taskdefs/War.java
+++ b/src/main/org/apache/tools/ant/taskdefs/War.java
@@ -219,7 +219,8 @@ public class War extends Jar {
         if (addedWebXmlFile == null
             && deploymentDescriptor == null
             && needxmlfile
-            && !isInUpdateMode()) {
+            && !isInUpdateMode()
+            && hasUpdatedFile()) {
             throw new BuildException("No WEB-INF/web.xml file was added.\n"
                     + "If this is your intent, set needxmlfile='false' ");
         }
diff --git a/src/main/org/apache/tools/ant/taskdefs/Zip.java b/src/main/org/apache/tools/ant/taskdefs/Zip.java
index 362a5cc83..52b142682 100644
--- a/src/main/org/apache/tools/ant/taskdefs/Zip.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Zip.java
@@ -97,6 +97,10 @@ public class Zip extends MatchingTask {
 
     // CheckStyle:VisibilityModifier ON
 
+    // This boolean is set if the task detects that the
+    // target is outofdate and has written to the target file.
+    private boolean updatedFile = false;
+
     /**
      * true when we are adding new files into the Zip file, as opposed
      * to adding back the unchanged files
@@ -411,6 +415,16 @@ public class Zip extends MatchingTask {
         }
     }
 
+    /**
+     * Get the value of the updatedFile attribute.
+     * This should only be called after executeMain has been
+     * called.
+     * @return true if executeMain has written to the zip file.
+     */
+    protected boolean hasUpdatedFile() {
+        return updatedFile;
+    }
+
     /**
      * Build the zip file.
      * This is called twice if doubleFilePass is true.
@@ -450,6 +464,7 @@ public class Zip extends MatchingTask {
             if (!state.isOutOfDate()) {
                 return;
             }
+            updatedFile = true;
             if (!zipFile.exists() && state.isWithoutAnyResources()) {
                 createEmptyZip(zipFile);
                 return;