diff --git a/slugify.sh b/slugify.sh
index 3dcb854..3b703d8 100755
--- a/slugify.sh
+++ b/slugify.sh
@@ -1,18 +1,26 @@
 #!/usr/bin/env bash
 
-KEY=${INPUT_KEY^^}
-CS_VALUE=${INPUT_VALUE:-${!INPUT_KEY}}
-VALUE=${CS_VALUE,,}
+if [[ "$OSTYPE" == "darwin"* ]]; then
+  # On MacOS,
+  # bash don't support substitution, so we use 'tr'
+  KEY=$(echo "$INPUT_KEY" | tr '[:lower:]' '[:upper:]')
+  CS_VALUE=${INPUT_VALUE:-${!INPUT_KEY}}
+  VALUE=$(echo "$CS_VALUE" | tr '[:upper:]' '[:lower:]')
+else
+  KEY=${INPUT_KEY^^}
+  CS_VALUE=${INPUT_VALUE:-${!INPUT_KEY}}
+  VALUE=${CS_VALUE,,}
+fi
 
 slug() {
   echo "$1" |
-    sed -r 's#refs/[^\/]*/##;s/[^a-zA-Z0-9._]+/-/g;s/^-*//;s/-*$//' |
+    sed -E 's#refs/[^\/]*/##;s/[^a-zA-Z0-9._]+/-/g;s/-+/-/g;s/^-*//;s/-*$//' |
     cut -c1-63
 }
 
 slug_url() {
   echo "$1" |
-    sed -r 's#refs/[^\/]*/##;s/[^a-zA-Z0-9_]+/-/g;s/^-//;s/-$//' |
+    sed -E 's#refs/[^\/]*/##;s/[^a-zA-Z0-9_]+/-/g;s/-+/-/g;s/^-*//;s/-*$//' |
     cut -c1-63
 }