--- a/AbstractOperatingSystem.st	Thu Mar 28 15:50:36 2019 +0100
+++ b/AbstractOperatingSystem.st	Thu Mar 28 16:00:29 2019 +0100
@@ -3134,9 +3134,12 @@
 
     |osErrorHolder parentDirName|
 
+    (self isDirectory:dirName) ifTrue:[
+        ^ nil.
+    ].
 
     (osErrorHolder := self createDirectory:dirName) isNil ifTrue:[
-        "no error"
+        "directory was created"
         aOneArgBlock notNil ifTrue:[        
             aOneArgBlock value:dirName asFilename.
         ].