diff --git a/lib/util/exec/docker/index.ts b/lib/util/exec/docker/index.ts
index 8ef7677e3b3921a95a707734558e01da8bdaa09a..37326e9aed0674727098114bb49cc03852bf44ab 100644
--- a/lib/util/exec/docker/index.ts
+++ b/lib/util/exec/docker/index.ts
@@ -205,7 +205,14 @@ export async function generateDockerCommand(
   if (options.tag) {
     tag = options.tag;
   } else if (tagConstraint) {
-    tag = await getDockerTag(image, tagConstraint, tagScheme || 'semver');
+    const versioning = tagScheme || 'semver';
+    tag = await getDockerTag(image, tagConstraint, versioning);
+    logger.debug(
+      { image, tagConstraint, versioning, tag },
+      'Resolved tag constraint'
+    );
+  } else {
+    logger.debug({ image }, 'No tag or tagConstraint specified');
   }
 
   const taggedImage = tag ? `${image}:${tag}` : `${image}`;