diff --git a/ClangFormat.cmake b/ClangFormat.cmake
index 789dd7b..7f2601b 100644
--- a/ClangFormat.cmake
+++ b/ClangFormat.cmake
@@ -5,7 +5,21 @@
 # use clang-format to format source code according to a configuration file. 2 types
 # of targets will be created, one for formatting all files in the repository and the
 # other for formatting only the files which differ from master. The list of files to
-# format is generated by git itself. 
+# format is generated by git itself using a GLOB pattern.
+#
+# The default pattern will include the following file types
+#  *.c *.h *.cpp *.cc *.hpp
+#
+# A project may provide a custom file matching pattern to override the default
+#
+# swift_setup_clang_format(PATTERNS '*.c')
+#
+# will format ONLY *.c files. It is possible to provide a path in the pattern
+#
+# swift_setup_clang_format(PATTERNS 'src/*.c' 'include/*.h')
+#
+# will format only *.c files under ${PROJECT_SOURCE_DIR}/src and *.h files under
+# ${PROJECT_SOURCE_DIR}/include
 #
 # The created targets have the names
 #
@@ -107,7 +121,7 @@ endmacro()
 function(swift_setup_clang_format)
   set(argOption "REQUIRED")
   set(argSingle "SCRIPT")
-  set(argMulti "CLANG_FORMAT_NAMES")
+  set(argMulti "CLANG_FORMAT_NAMES" "PATTERNS")
 
   cmake_parse_arguments(x "${argOption}" "${argSingle}" "${argMulti}" ${ARGN})
 
@@ -197,12 +211,16 @@ function(swift_setup_clang_format)
   message(STATUS "Using ${CLANG_FORMAT}")
   set(${PROJECT_NAME}_CLANG_FORMAT ${CLANG_FORMAT} CACHE STRING "Absolute path to clang-format for ${PROJECT_NAME}")
 
-  # Format all source and header files in the repo, use a git command to build the file list
-  set(default_patterns '*.[ch]' '*.cpp' '*.cc' '*.hpp')
+  if(x_PATTERNS)
+    set(patterns ${x_PATTERNS})
+  else()
+    # Format all source and header files in the repo, use a git command to build the file list
+    set(patterns '*.[ch]' '*.cpp' '*.cc' '*.hpp')
+  endif()
 
   create_targets(
       TOP_LEVEL ${top_level_project}
-      ALL_COMMAND git ls-files ${default_patterns} | xargs ${${PROJECT_NAME}_CLANG_FORMAT} -i
-      DIFF_COMMAND git diff --diff-filter=ACMRTUXB --name-only master -- ${default_patterns} | xargs ${${PROJECT_NAME}_CLANG_FORMAT} -i
+      ALL_COMMAND git ls-files ${patterns} | xargs ${${PROJECT_NAME}_CLANG_FORMAT} -i
+      DIFF_COMMAND git diff --diff-filter=ACMRTUXB --name-only master -- ${patterns} | xargs ${${PROJECT_NAME}_CLANG_FORMAT} -i
   )
 endfunction()