diff --git a/src/osgViewer/ViewerBase.cpp b/src/osgViewer/ViewerBase.cpp
index 7f5049616..743d6d2dd 100644
--- a/src/osgViewer/ViewerBase.cpp
+++ b/src/osgViewer/ViewerBase.cpp
@@ -328,7 +328,7 @@ void ViewerBase::startThreading()
         }
     }
 
-    int numProcessors = OpenThreads::GetNumberOfProcessors();
+    int numProcessors = osg::minimum(1, OpenThreads::GetNumberOfProcessors());
     bool affinity = numProcessors>1;
 
     Contexts::iterator citr;