diff --git a/Makefile b/Makefile
index 0dd8524..f123d87 100644
--- a/Makefile
+++ b/Makefile
@@ -14,9 +14,12 @@ serve:
 	hugo server -D -F
 
 deploy:
-	@if [ -n "$$KEY" ]; then eval "$$(ssh-agent)"; echo "$$KEY" | ssh-add -; fi
-	if [ -z "$$USERNAME" ] || [ -z "$$SSH_HOST" ] || [ -z "$$TARGET" ]; then exit 1; fi
-	rsync --progress -avz --delete public/ "$$USERNAME@$$SSH_HOST:$$TARGET"
+	@if [ -n "$$SSH_KEY" ]; then eval "$$(ssh-agent)"; echo "$$SSH_KEY" | ssh-add -; fi
+	@if [ -z "$$SSH_USER" ] || [ -z "$$SSH_HOST" ] || [ -z "$$SSH_TARGET" ]; \
+		then echo "Missing one of SSH_USER, SSH_HOST, or TARGET" >&2; \
+		exit 1; \
+	fi
+	rsync --progress -avz --delete public/ "$$SSH_USER@$$SSH_HOST:$$TARGET"
 
 .PHONY: clean
 clean: