diff --git a/scripts/brotli-wrapper.sh b/scripts/brotli-wrapper.sh
new file mode 100644
index 0000000..ca3d163
--- /dev/null
+++ b/scripts/brotli-wrapper.sh
@@ -0,0 +1,8 @@
+#!/bin/sh
+# compress a file with brotli if it isn't already compressed. 
+set -e -u
+
+if [ ! -f "$1.br" ]; then
+	brotli -Z -- "$1"
+fi
+
diff --git a/scripts/compress.sh b/scripts/compress.sh
index 6b68660..817a754 100644
--- a/scripts/compress.sh
+++ b/scripts/compress.sh
@@ -5,18 +5,19 @@
 # 2. "gzip" or "brotli"
 # 3. ECT zopfli compression level
 
-# no pipefail here since there are no pipes.
+#shellcheck disable=SC3040  # This only sets pipefail if it's available and otherwise does nothing
+set -o pipefail 2>/dev/null || true
 set -e -u
 
+dirname="$(dirname "$0")"
 output_dir="$1"
 format="$2"
 
 alias find_compressible='find "$output_dir" -type f \( -name "*.html" -o -name "*.txt" -o -name "*.xml" -o -name "*.webmanifest" -o -name "*.*.svg" -o -name "*.json" \)'
 
 if [ "$format" = "gzip" ]; then
-	compress_level="$3"
-	find_compressible -exec ect -quiet -"$compress_level" -gzip {} \;
-	find_compressible -exec touch -r {} {}.gz \;
-elif [ "$2" = "brotli" ]; then
-	find_compressible -exec brotli -Z -- {} \;
+	# compression level should be the third argument
+	find_compressible | xargs -n1 sh "$dirname/ect-wrapper.sh" "${3-6}"
+elif [ "$format" = "brotli" ]; then
+	find_compressible | xargs -n1 sh "$dirname/brotli-wrapper.sh"
 fi
diff --git a/scripts/ect-wrapper.sh b/scripts/ect-wrapper.sh
new file mode 100644
index 0000000..d6dc945
--- /dev/null
+++ b/scripts/ect-wrapper.sh
@@ -0,0 +1,9 @@
+#!/bin/sh
+# compress a file with ect and preserve the mtime
+# args: compression level and filename.
+set -e -u
+
+if [ ! -f "$2.gz" ]; then
+	ect -quiet -"$1" -gzip "$2"
+	touch -r "$2" "$2.gz"
+fi