diff --git a/doc/Doxyfile.in b/doc/Doxyfile.in
index 51e0a262b22..669d22ea580 100644
--- a/doc/Doxyfile.in
+++ b/doc/Doxyfile.in
@@ -291,7 +291,7 @@ OPTIMIZE_OUTPUT_VHDL   = NO
 # Note that for custom extensions you also need to set FILE_PATTERNS otherwise
 # the files are not read by doxygen.
 
-EXTENSION_MAPPING      = F90=FortranFree, f90=FortranFree 
+EXTENSION_MAPPING      = f90=FortranFree,F90=FortranFree 
 
 # If the MARKDOWN_SUPPORT tag is enabled then doxygen pre-processes all comments
 # according to the Markdown format, which allows for more readable