diff --git a/behave/features/checkconstraints.feature b/behave/features/checkconstraints.feature
new file mode 100644
index 00000000..e2c7803e
--- /dev/null
+++ b/behave/features/checkconstraints.feature
@@ -0,0 +1,18 @@
+Feature: `osc checkconstraints` command
+
+
+# common steps for all scenarios
+Background:
+   Given I set working directory to "{context.osc.temp}"
+
+
+Scenario: Run `osc checkconstraints <project>/<package> <repository>/<arch>`
+    When I execute osc with args "checkconstraints test:factory/test-pkgA standard/x86_64"
+    Then the exit code is 0
+
+
+Scenario: Run `osc checkconstraints` from a package working copy
+   Given I execute osc with args "co test:factory/test-pkgA"
+     And I set working directory to "{context.osc.temp}/test:factory/test-pkgA"
+    When I execute osc with args "checkconstraints"
+    Then the exit code is 0
diff --git a/osc/connection.py b/osc/connection.py
index 630b7892..86f7a3fc 100644
--- a/osc/connection.py
+++ b/osc/connection.py
@@ -288,9 +288,10 @@ def http_request(method: str, url: str, headers=None, data=None, file=None):
     # https://github.com/openSUSE/open-build-service/pull/13019
     headers.add("Accept", "application/xml")
 
-    if data or file:
-        # osc/obs data is usually XML
+    if method == "PUT" or (method == "POST" and (data or file)):
         headers.add("Content-Type", "application/xml; charset=utf-8")
+    elif method == "POST":
+        headers.add("Content-Type", "application/x-www-form-urlencoded")
 
     if purl.scheme == "http" and HTTP_PROXY_MANAGER:
         # HTTP proxy requires full URL with 'same host' checking off