diff --git a/readthedocs/core/unresolver.py b/readthedocs/core/unresolver.py
index 1aa2986a34f..65c0d387b2e 100644
--- a/readthedocs/core/unresolver.py
+++ b/readthedocs/core/unresolver.py
@@ -445,45 +445,38 @@ def unresolve_domain(self, domain):
         subdomain, *root_domain = domain.split(".", maxsplit=1)
         root_domain = root_domain[0] if root_domain else ""
 
-        if public_domain in domain:
-            # Serve from the PUBLIC_DOMAIN, ensuring it looks like `foo.PUBLIC_DOMAIN`.
-            if public_domain == root_domain:
-                project_slug = subdomain
-                log.debug("Public domain.", domain=domain)
+        # Serve from the PUBLIC_DOMAIN, ensuring it looks like `foo.PUBLIC_DOMAIN`.
+        if public_domain == root_domain:
+            project_slug = subdomain
+            log.debug("Public domain.", domain=domain)
+            return UnresolvedDomain(
+                source_domain=domain,
+                source=DomainSourceType.public_domain,
+                project=self._resolve_project_slug(project_slug, domain),
+            )
+
+        # Serve from the RTD_EXTERNAL_VERSION_DOMAIN, ensuring it looks like
+        # `project--version.RTD_EXTERNAL_VERSION_DOMAIN`.
+        if external_domain == root_domain:
+            try:
+                project_slug, version_slug = subdomain.rsplit("--", maxsplit=1)
+                log.debug("External versions domain.", domain=domain)
                 return UnresolvedDomain(
                     source_domain=domain,
-                    source=DomainSourceType.public_domain,
+                    source=DomainSourceType.external_domain,
                     project=self._resolve_project_slug(project_slug, domain),
+                    external_version_slug=version_slug,
                 )
+            except ValueError:
+                log.info("Invalid format of external versions domain.", domain=domain)
+                raise InvalidExternalDomainError(domain=domain)
 
+        if public_domain in domain or external_domain in domain:
             # NOTE: This can catch some possibly valid domains (docs.readthedocs.io.com)
             # for example, but these might be phishing, so let's block them for now.
             log.warning("Weird variation of our domain.", domain=domain)
             raise SuspiciousHostnameError(domain=domain)
 
-        # Serve PR builds on external_domain host.
-        if external_domain in domain:
-            if external_domain == root_domain:
-                try:
-                    project_slug, version_slug = subdomain.rsplit("--", maxsplit=1)
-                    log.debug("External versions domain.", domain=domain)
-                    return UnresolvedDomain(
-                        source_domain=domain,
-                        source=DomainSourceType.external_domain,
-                        project=self._resolve_project_slug(project_slug, domain),
-                        external_version_slug=version_slug,
-                    )
-                except ValueError:
-                    log.info(
-                        "Invalid format of external versions domain.", domain=domain
-                    )
-                    raise InvalidExternalDomainError(domain=domain)
-
-            # NOTE: This can catch some possibly valid domains (docs.readthedocs.build.com)
-            # for example, but these might be phishing, so let's block them for now.
-            log.warning("Weird variation of our domain.", domain=domain)
-            raise SuspiciousHostnameError(domain=domain)
-
         # Custom domain.
         domain_object = (
             Domain.objects.filter(domain=domain).select_related("project").first()
diff --git a/readthedocs/rtd_tests/tests/test_unresolver.py b/readthedocs/rtd_tests/tests/test_unresolver.py
index 9708a523919..4011657f80a 100644
--- a/readthedocs/rtd_tests/tests/test_unresolver.py
+++ b/readthedocs/rtd_tests/tests/test_unresolver.py
@@ -323,3 +323,27 @@ def test_unresolver_suspicious_hostname(self):
 
         with pytest.raises(SuspiciousHostnameError):
             unresolve("https://dev.readthedocs.build.phishing.com/en/latest/")
+
+    @override_settings(
+        PUBLIC_DOMAIN="readthedocs.dev",
+        RTD_EXTERNAL_VERSION_DOMAIN="build.readthedocs.dev",
+    )
+    def test_unresolve_overlapping_public_and_external_domains(self):
+        external_version = get(
+            Version,
+            project=self.pip,
+            type=EXTERNAL,
+            slug="10",
+            active=True,
+        )
+        parts = unresolve("https://pip.readthedocs.dev/en/latest/")
+        self.assertEqual(parts.parent_project, self.pip)
+        self.assertEqual(parts.project, self.pip)
+        self.assertEqual(parts.version, self.version)
+        self.assertEqual(parts.filename, "/index.html")
+
+        parts = unresolve("https://pip--10.build.readthedocs.dev/en/10/")
+        self.assertEqual(parts.parent_project, self.pip)
+        self.assertEqual(parts.project, self.pip)
+        self.assertEqual(parts.version, external_version)
+        self.assertEqual(parts.filename, "/index.html")