diff --git a/doc/Doxyfile.in b/doc/Doxyfile.in
index 53a1c78ee2..0086929fc6 100644
--- a/doc/Doxyfile.in
+++ b/doc/Doxyfile.in
@@ -298,7 +298,8 @@ TYPEDEF_HIDES_STRUCT   = NO
 # 2^(16+SYMBOL_CACHE_SIZE). The valid range is 0..9, the default is 0,
 # corresponding to a cache size of 2^16 = 65536 symbols
 
-SYMBOL_CACHE_SIZE      = 0
+# Deprecated, so removing this to prevent a warning in Doxygen.
+# SYMBOL_CACHE_SIZE      = 0
 
 #---------------------------------------------------------------------------
 # Build related configuration options