diff --git a/doc/doxygen.conf b/doc/doxygen.conf
index e8bb803de..05f7d0662 100644
--- a/doc/doxygen.conf
+++ b/doc/doxygen.conf
@@ -474,7 +474,7 @@ LOOKUP_CACHE_SIZE      = 2
 # DOT_NUM_THREADS setting.
 # Minimum value: 0, maximum value: 32, default value: 1.
 
-NUM_PROC_THREADS       = 0
+NUM_PROC_THREADS       = 1
 
 #---------------------------------------------------------------------------
 # Build related configuration options