diff --git a/lib/blacklist.js b/lib/blacklist.js
index 7b127bd..fefc72e 100644
--- a/lib/blacklist.js
+++ b/lib/blacklist.js
@@ -107,6 +107,27 @@ function firmaSlug(s) {
   return (kept.length ? kept : words).join('-');
 }
 
+// Do two company slugs refer to the SAME employer? True when they are equal, or
+// when the shorter one's hyphen tokens are a leading prefix of the longer one's.
+// The prefix rule collapses "short name" vs "full legal name" spellings of one
+// firm — e.g. "it-problemloeser" vs "it-problemloeser-verwaltungs-und-handels",
+// or "stadtwerke-essen" vs "stadtwerke-essen-netz". To avoid merging distinct
+// firms that merely share a first word ("meyer-it" vs "meyer-logistik"), a pure
+// prefix match requires the shorter slug to carry at least two tokens; a
+// single-token slug only matches an identical one.
+function sameCompany(a, b) {
+  if (!a || !b) return false;
+  if (a === b) return true;
+  const ta = String(a).split('-').filter(Boolean);
+  const tb = String(b).split('-').filter(Boolean);
+  const [short, long] = ta.length <= tb.length ? [ta, tb] : [tb, ta];
+  if (short.length < 2) return false; // single distinctive token → exact only
+  for (let i = 0; i < short.length; i++) {
+    if (short[i] !== long[i]) return false;
+  }
+  return true;
+}
+
 // Normalise a company / job-title string for fuzzy identity matching:
 // unescape, lowercase, drop gender markers like "(m/w/d)", collapse anything
 // non-alphanumeric to single spaces.
@@ -138,10 +159,12 @@ function offerSignature(offer) {
   };
 }
 
-// Company identity match: prefer the robust slug, fall back to firma_norm for
-// legacy rows written before firma_slug existed (or not yet backfilled).
+// Company identity match: prefer the robust slug (equal or prefix — see
+// sameCompany, which absorbs spelling / legal-form / umlaut variants of one
+// employer), fall back to firma_norm for legacy rows written before firma_slug
+// existed (or not yet backfilled).
 function firmaMatch(row, sig) {
-  if (row.firma_slug && sig.firma_slug) return row.firma_slug === sig.firma_slug;
+  if (row.firma_slug && sig.firma_slug) return sameCompany(row.firma_slug, sig.firma_slug);
   return !!row.firma_norm && row.firma_norm === sig.firma_norm;
 }
 
@@ -259,6 +282,7 @@ module.exports = {
   urlDomain,
   normText,
   firmaSlug,
+  sameCompany,
   offerSignature,
   rowMatches,
   matchBlacklist,