diff --git a/WHATSNEW b/WHATSNEW
index 0a897b3b3..ca2160ebc 100644
--- a/WHATSNEW
+++ b/WHATSNEW
@@ -124,6 +124,9 @@ Fixed bugs:
 * Execution of top level tasks in imported files get delayed by targets.
   Bugzilla report 31487.
 
+* ExecTask executes checkConfiguration() even though os does not match.
+  Bugzilla report 31805.
+
 Changes from Ant 1.6.1 to Ant 1.6.2
 ===================================
 
diff --git a/src/main/org/apache/tools/ant/taskdefs/ExecTask.java b/src/main/org/apache/tools/ant/taskdefs/ExecTask.java
index 963cbb8de..229d60dbc 100644
--- a/src/main/org/apache/tools/ant/taskdefs/ExecTask.java
+++ b/src/main/org/apache/tools/ant/taskdefs/ExecTask.java
@@ -455,15 +455,17 @@ public class ExecTask extends Task {
      * </ul>
      */
     public void execute() throws BuildException {
+        // Quick fail if this is not a valid OS for the command
+        if (!isValidOs()) {
+            return;
+        }
         File savedDir = dir; // possibly altered in prepareExec
         cmdl.setExecutable(resolveExecutable(executable, searchPath));
         checkConfiguration();
-        if (isValidOs()) {
-            try {
-                runExec(prepareExec());
-            } finally {
-                dir = savedDir;
-            }
+        try {
+            runExec(prepareExec());
+        } finally {
+            dir = savedDir;
         }
     }