diff --git a/src/osgPlugins/shp/ESRIShape.cpp b/src/osgPlugins/shp/ESRIShape.cpp
index 32c87d6bf..49eb18d44 100644
--- a/src/osgPlugins/shp/ESRIShape.cpp
+++ b/src/osgPlugins/shp/ESRIShape.cpp
@@ -838,7 +838,7 @@ bool PointZ::read( int fd )
         return false;
 
     // Sometimes, M field is not supplied
-    if( rh.contentLength >= 18 )
+    if( rh.contentLength*2 >= 18 )
         if( readVal<Double>( fd, m, LittleEndian ) == false )
             return false;