diff --git a/lib/finalize-db.js b/lib/finalize-db.js
index 8679a7d0f..f73bb4951 100644
--- a/lib/finalize-db.js
+++ b/lib/finalize-db.js
@@ -73,12 +73,12 @@ async function resolveQueryLanguages(codeqlCmd, config) {
         const noDeclaredLanguage = resolveQueriesOutputObject.noDeclaredLanguage;
         const noDeclaredLanguageQueries = Object.keys(noDeclaredLanguage);
         if (noDeclaredLanguageQueries.length !== 0) {
-            core.warning('Some queries do not declare a language:\n' + noDeclaredLanguageQueries.join('\n'));
+            throw new Error('Some queries do not declare a language, their qlpack.yml file is missing or is invalid');
         }
         const multipleDeclaredLanguages = resolveQueriesOutputObject.multipleDeclaredLanguages;
         const multipleDeclaredLanguagesQueries = Object.keys(multipleDeclaredLanguages);
         if (multipleDeclaredLanguagesQueries.length !== 0) {
-            core.warning('Some queries declare multiple languages:\n' + multipleDeclaredLanguagesQueries.join('\n'));
+            throw new Error('Some queries declare multiple languages, their qlpack.yml file is missing or is invalid');
         }
     }
     return res;
diff --git a/src/finalize-db.ts b/src/finalize-db.ts
index a03e68a1b..b9605b0e2 100644
--- a/src/finalize-db.ts
+++ b/src/finalize-db.ts
@@ -82,13 +82,13 @@ async function resolveQueryLanguages(codeqlCmd: string, config: configUtils.Conf
     const noDeclaredLanguage = resolveQueriesOutputObject.noDeclaredLanguage;
     const noDeclaredLanguageQueries = Object.keys(noDeclaredLanguage);
     if (noDeclaredLanguageQueries.length !== 0) {
-      core.warning('Some queries do not declare a language:\n' + noDeclaredLanguageQueries.join('\n'));
+      throw new Error('Some queries do not declare a language, their qlpack.yml file is missing or is invalid');
     }
 
     const multipleDeclaredLanguages = resolveQueriesOutputObject.multipleDeclaredLanguages;
     const multipleDeclaredLanguagesQueries = Object.keys(multipleDeclaredLanguages);
     if (multipleDeclaredLanguagesQueries.length !== 0) {
-      core.warning('Some queries declare multiple languages:\n' + multipleDeclaredLanguagesQueries.join('\n'));
+      throw new Error('Some queries declare multiple languages, their qlpack.yml file is missing or is invalid');
     }
   }