diff --git a/CHANGELOG.md b/CHANGELOG.md
index a9251fd..52f747d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
 
 ### Changed
 
+- The publish job and `task publish` refuse to run while `ECCENCA_MARKETPLACE_URL` is unset: without it `cmemc package publish` publishes to `https://eccenca.market`, so a package meant for a self-hosted marketplace went public on its first merge to main. A package published to eccenca.market sets `ECCENCA_MARKETPLACE_URL=https://eccenca.market` in its CI variables once
 - The `shapes` skill says that a class the package does not own - from a vocabulary it ships unchanged or depends on, such as QUDT or FOAF - gets its icon from a `foaf:depiction` on the package's node shape, so its resources show an icon in Explore without the package changing the source's vocabulary; the `vocabulary` skill's depictions reference points there
 
 ## [1.8.0] 2026-10-18
diff --git a/README.md b/README.md
index 3d47b85..ab6277f 100644
--- a/README.md
+++ b/README.md
@@ -91,7 +91,7 @@ copier copy -r develop gh:eccenca/cmem-package-template your-new-vocabulary-pack
 | `package_description` | Short description | - |
 | `python_dependencies` | Comma-separated Python package dependencies (project packages only) | - |
 | `vocab_dependencies` | Comma-separated vocabulary/project dependencies (project packages only) | - |
-| `marketplace` | Publish this package to the marketplace? A no leaves the publish job out of `.gitlab-ci.yml` | `true` |
+| `marketplace` | Publish this package to a marketplace? The publish job and `task publish` publish to the marketplace `ECCENCA_MARKETPLACE_URL` names and refuse to run without it; a no leaves the publish job out of `.gitlab-ci.yml` | `true` |
 | `github_page` | Link to GitHub page of the package | - |
 
 ## Generated Structure
diff --git a/copier.yaml b/copier.yaml
index 7019234..d2378e5 100644
--- a/copier.yaml
+++ b/copier.yaml
@@ -75,9 +75,11 @@ marketplace:
   type: bool
   default: true
   help: >-
-    marketplace: Will this package be published to the eccenca marketplace?
-    Answer no for internal packages - the publish job is then left out of
-    the generated .gitlab-ci.yml.
+    marketplace: Will this package be published to a marketplace? The
+    publish job publishes to the marketplace ECCENCA_MARKETPLACE_URL names
+    (https://eccenca.market for a public package) and refuses to run without
+    it. Answer no for packages nobody publishes - the publish job is then
+    left out of the generated .gitlab-ci.yml.
 
 github_page:
   type: str
diff --git a/src/.gitlab-ci.yml.jinja b/src/.gitlab-ci.yml.jinja
index e4c93e1..1828250 100644
--- a/src/.gitlab-ci.yml.jinja
+++ b/src/.gitlab-ci.yml.jinja
@@ -51,6 +51,9 @@ publish:
       elif [ -z "${ECCENCA_MARKETPLACE_ACCOUNT}" ]; then
         echo "ECCENCA_MARKETPLACE_ACCOUNT not available ..."
         exit 1
+      elif [ -z "${ECCENCA_MARKETPLACE_URL}" ]; then
+        echo "ECCENCA_MARKETPLACE_URL not available: name the marketplace this package publishes to (https://eccenca.market for a public package) ..."
+        exit 1
       else
         task publish
       fi
diff --git a/src/Taskfile.yaml b/src/Taskfile.yaml
index 200964c..aa461e4 100644
--- a/src/Taskfile.yaml
+++ b/src/Taskfile.yaml
@@ -116,6 +116,11 @@ tasks:
         msg: >
           No package archive for version {{.PACKAGE_VERSION}} found in
           {{.DIST_DIR}}. Run 'task build' first.
+      - sh: test -n "${ECCENCA_MARKETPLACE_URL}"
+        msg: >
+          ECCENCA_MARKETPLACE_URL is not set. Name the marketplace this package
+          publishes to (https://eccenca.market for a public package): without it
+          cmemc publishes to https://eccenca.market.
     cmds:
       - cmemc package publish {{.DIST_DIR}}/{{.PACKAGE_ID}}-{{.PACKAGE_VERSION}}.cpa