diff --git a/README.md b/README.md
index e9e47c0..5daa7aa 100644
--- a/README.md
+++ b/README.md
@@ -27,4 +27,5 @@ URL=https://idp.example.com/idp/profile/SAML2/SOAP/ECP \
 bash test.sh | xmllint --pretty 1 -
 ```
 
-
+You can also override the HTTP `Content-Type` in the request by setting
+`CONTENT_TYPE` environment variables.
diff --git a/test.sh b/test.sh
index 40bf47c..2087f54 100755
--- a/test.sh
+++ b/test.sh
@@ -24,6 +24,6 @@ echo $REQUEST | xmllint --pretty 1 -
 echo $REQUEST |
 	curl -k \
 		-d @- \
-		-H "Content-Type: text/xml" \
+		-H "Content-Type: ${CONTENT_TYPE:-text/xml}" \
 		--basic -u $CRED \
 		$URL