diff --git a/industrial_ci/src/tests/merge_fixes.py b/industrial_ci/src/tests/merge_fixes.py
index 73ad4ad94..afba1cda6 100755
--- a/industrial_ci/src/tests/merge_fixes.py
+++ b/industrial_ci/src/tests/merge_fixes.py
@@ -20,6 +20,13 @@
 import sys
 
 
+def key(item):
+   name = item.get("DiagnosticName")
+   msg = item.get("DiagnosticMessage")
+   file = msg.get("FilePath")
+   offset = msg.get("FileOffset")
+   return name, file, offset
+
 def merge_fixes(files):
    """Merge all fixes files into mergefile"""
    # The fixes suggested by clang-tidy >= 4.0.0 are given under
@@ -27,13 +34,22 @@ def merge_fixes(files):
    mergefile = files[0]
    mergekey = "Diagnostics"
    merged = []
+   seen = set()  # efficiently remember fixes already inserted
+
+   def have(x):
+      k = key(x)
+      return k in seen or seen.add(k)
+
+   def unique(seq):
+      return [x for x in seq if not have(x)]
+
    for file in files:
       try:
          with open(file, 'r') as inp:
             content = yaml.safe_load(inp)
             if not content:
                continue  # Skip empty files.
-            merged.extend(content.get(mergekey, []))
+            merged.extend(unique(content.get(mergekey, [])))
       except FileNotFoundError:
          pass