https://github.com/ImageMagick/ImageMagick6/issues/43

diff --git a/MagickCore/blob.c b/MagickCore/blob.c
index 7de1023f69ce16d6a7c67e19a2cb843eb8a95f3c..70760a83b687bceac20215fe29034f475e211f98 100644 (file)
--- a/MagickCore/blob.c
+++ b/MagickCore/blob.c
@@ -996,6 +996,7 @@ MagickExport void *DetachBlob(BlobInfo *blob_info)
   if (blob_info->mapped != MagickFalse)
     {
       (void) UnmapBlob(blob_info->data,blob_info->length);
+      blob_info->data=NULL;
       RelinquishMagickResource(MapResource,blob_info->length);
     }
   blob_info->mapped=MagickFalse;