diff --git a/doc/doxygen.conf b/doc/doxygen.conf
index 9306cf4aa..341a7b600 100644
--- a/doc/doxygen.conf
+++ b/doc/doxygen.conf
@@ -461,7 +461,7 @@ TYPEDEF_HIDES_STRUCT   = YES
 # the optimal cache size from a speed point of view.
 # Minimum value: 0, maximum value: 9, default value: 0.
 
-LOOKUP_CACHE_SIZE      = 2
+LOOKUP_CACHE_SIZE      = 4
 
 # The NUM_PROC_THREADS specifies the number threads doxygen is allowed to use
 # during processing. When set to 0 doxygen will based this on the number of