diff --git a/Doxyfile b/Doxyfile
index 0e4cdc068..e157cf4d0 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -1197,7 +1197,9 @@ INPUT_FILTER           =
 # need to set EXTENSION_MAPPING for the extension otherwise the files are not
 # properly processed by Doxygen.
 
-FILTER_PATTERNS        = "*.proto="python doc/doxygen/filters/proto2cpp.py"
+FILTER_PATTERNS        = "*.proto=" \
+                         python \
+                         "doc/doxygen/filters/proto2cpp.py"
 
 # If the FILTER_SOURCE_FILES tag is set to YES, the input filter (if set using
 # INPUT_FILTER) will also be used to filter the input files that are used for