--- a/PipeStream.st	Thu Dec 29 21:25:18 2016 +0100
+++ b/PipeStream.st	Fri Dec 30 13:07:37 2016 +0100
@@ -657,7 +657,7 @@
                     directory:aDirectory.
 
     mode == #readwrite ifTrue:[
-        pipeArray := NonPositionableExternalStream makeBidirectionalPipe.
+        pipeArray := self class makeBidirectionalPipe.
         pipeArray isNil ifTrue:[
             lastErrorNumber := errorNumber := OperatingSystem currentErrorNumber.
             ^ self openError:errorNumber.
@@ -667,7 +667,7 @@
         osProcess inStream:remotePipeEnd.
         osProcess outStream:remotePipeEnd.
     ] ifFalse:[
-        pipeArray := NonPositionableExternalStream makePipe.
+        pipeArray := self class makePipe.
         pipeArray isNil ifTrue:[
             lastErrorNumber := errorNumber := OperatingSystem currentErrorNumber.
             ^ self openError:errorNumber.
@@ -691,7 +691,7 @@
         osProcess errorStream:nullOutput.
     ] ifFalse:[(errorDisposition == #inline or:[errorDisposition == #stdout]) ifTrue:[
         osProcess errorStream:osProcess outStream.
-    ] ifFalse:[(errorDisposition == #stderr or:[errorDisposition == nil]) ifTrue:[
+    ] ifFalse:[(errorDisposition == #stderr or:[errorDisposition isNil]) ifTrue:[
         osProcess errorStream:Stderr.
     ] ifFalse:[errorDisposition isStream ifTrue:[
         osProcess errorStream:errorDisposition.