diff --git a/.githooks/pre-commit b/.githooks/pre-commit
index 22a39f77..4cc182b1 100755
--- a/.githooks/pre-commit
+++ b/.githooks/pre-commit
@@ -1,13 +1,23 @@
 #!/bin/bash
 
+if git rev-parse --verify HEAD >/dev/null 2>&1; then
+    against=HEAD
+else
+    # Initial commit: diff against an empty tree object
+    against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+fi
+
 # fail if we add any new lines to C or Scheme source containing a tab
-if git diff --name-only | egrep '\.(cpp|h|scm|sld|stub)$' | xargs -d'\n' git diff -U0 -- | grep -q $'^+ *\t'; then
+if git diff --name-only "$against" |\
+        egrep '\.(cpp|h|scm|sld|stub)$' |\
+        xargs -d'\n' git diff -U0 --no-color  "$against" -- |\
+        grep -q $'^+ *\t'; then
     echo "Error: Attempting to add a source file using tabs for indentation."
     echo
     echo -n "   "
-    git diff --name-only |\
+    git diff --name-only "$against" |\
         egrep '\.(cpp|h|scm|sld|stub)$' |\
-        xargs -d'\n' git diff -U0 -- |\
+        xargs -d'\n' git diff -U0  "$against" -- |\
         grep $'^+ *\t' | head -1
     echo
     cat <<EOF