diff --git a/.githooks/pre-commit b/.githooks/pre-commit
new file mode 100755
index 00000000..22a39f77
--- /dev/null
+++ b/.githooks/pre-commit
@@ -0,0 +1,19 @@
+#!/bin/bash
+
+# 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 $'^+ *\t'; then
+    echo "Error: Attempting to add a source file using tabs for indentation."
+    echo
+    echo -n "   "
+    git diff --name-only |\
+        egrep '\.(cpp|h|scm|sld|stub)$' |\
+        xargs -d'\n' git diff -U0 -- |\
+        grep $'^+ *\t' | head -1
+    echo
+    cat <<EOF
+It's important for arguments to line up vertically to a precise column.
+Since there is no standard tab width, using tabs for indentation makes
+this impossible in general.  Please use spaces.
+EOF
+    exit 1
+fi
diff --git a/.githooks/update b/.githooks/update
deleted file mode 100755
index 2a0dbca1..00000000
--- a/.githooks/update
+++ /dev/null
@@ -1,10 +0,0 @@
-#!/bin/sh
-
-old="$2"
-new="$3"
-
-# fail if we add any new lines to C or Scheme source containing a tab
-git diff --name-only "$old" "$new" |\
-    egrep '\.(cpp|h|scm|sld|stub)$' |\
-    xargs -d'\n' git diff -U0 "$old" "$new" -- |\
-    grep -q $'^+.*\t' && exit 1