diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 2c8473190..e73bc3446 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -40,7 +40,9 @@ The following sections discuss the specific rules for the style that should be u
 make style
 ```
 
-before commiting your change. If you've already committed your changes that's okay since it will then check the files in the most recent commit. This can be useful after you've merged someone elses change and want to check that it's style is acceptable.
+before commiting your change. That will run `git-clang-format` to rewrite just the lines you're modifying.
+
+If you've already committed your changes that's okay since it will then check the files in the most recent commit. This can be useful after you've merged someone elses change and want to check that it's style is acceptable. However, in that case it will run `clang-format` to ensure the entire file, not just the lines modified by the commit, conform to the style.
 
 If you want to check the style of the entire code base run
 
@@ -48,6 +50,8 @@ If you want to check the style of the entire code base run
 make style-all
 ```
 
+That command will refuse to restyle any files if you have uncommitted changes.
+
 ### Suppressing Reformatting of the Code
 
 If you have a good reason for doing so you can tell `clang-format` to not reformat a block of code by enclosing it in comments like this:
diff --git a/build_tools/style.fish b/build_tools/style.fish
index 76cf920d5..62d8d5c7e 100755
--- a/build_tools/style.fish
+++ b/build_tools/style.fish
@@ -6,6 +6,7 @@
 # This runs C++ files and fish scripts (*.fish) through their respective code
 # formatting programs.
 #
+set git_clang_format no
 set c_files
 set f_files
 set all no
@@ -21,17 +22,21 @@ if set -q argv[1]
 end
 
 if test $all = yes
+    set files (git status --porcelain --short --untracked-files=all | sed -e 's/^ *[^ ]* *//')
+    if set -q files[1]
+        echo
+        echo You have uncommited changes. Cowardly refusing to restyle the entire code base.
+        echo
+        exit 1
+    end
     set c_files src/*.h src/*.cpp
     set f_files ***.fish
 else
-    # We haven't been asked to reformat all the source. If there are uncommitted
-    # changes reformat those, else reformat the files in the most recent commit.
-    set pending (git status --porcelain --short --untracked-files=all | sed -e 's/^ *//')
-    if count $pending > /dev/null
-        # There are pending changes so lint those files.
-        for arg in $pending
-            set files $files (string split -m 1 ' ' $arg)[2]
-        end
+    # We haven't been asked to reformat all the source. If there are uncommitted changes reformat
+    # those using `git clang-format`. Else reformat the files in the most recent commit.
+    set files (git status --porcelain --short --untracked-files=all | sed -e 's/^ *[^ ]* *//')
+    if set -q files[1]
+        set git_clang_format yes
     else
         # No pending changes so lint the files in the most recent commit.
         set files (git show --name-only --pretty=oneline head | tail --lines=+2)
@@ -45,18 +50,32 @@ end
 
 # Run the C++ reformatter if we have any C++ files.
 if set -q c_files[1]
-    if type -q clang-format
+    if test $git_clang_format = yes
+        if type -q git-clang-format
+            echo
+            echo ========================================
+            echo Running git-clang-format
+            echo ========================================
+            git add $c_files
+            git-clang-format
+        else
+            echo
+            echo 'WARNING: Cannot find git-clang-format command'
+            echo
+        end
+    else if type -q clang-format
         echo
         echo ========================================
         echo Running clang-format
         echo ========================================
         for file in $c_files
-            clang-format $file > $file.new
+            clang-format $file >$file.new
             if cmp --quiet $file $file.new
                 echo $file was correctly formatted
                 rm $file.new
             else
                 echo $file was NOT correctly formatted
+                chmod --reference=$file $file.new
                 mv $file.new $file
             end
         end
@@ -78,12 +97,13 @@ if set -q f_files[1]
     echo Running fish_indent
     echo ========================================
     for file in $f_files
-        fish_indent < $file > $file.new
+        fish_indent <$file >$file.new
         if cmp --quiet $file $file.new
             echo $file was correctly formatted
             rm $file.new
         else
             echo $file was NOT correctly formatted
+            chmod --reference=$file $file.new
             mv $file.new $file
         end
     end