diff --git a/plugins/axiomcode/skills/axiomcode/scripts/ax_fresh.py b/plugins/axiomcode/skills/axiomcode/scripts/ax_fresh.py
index 808b4a3cb..4993e7ccd 100644
--- a/plugins/axiomcode/skills/axiomcode/scripts/ax_fresh.py
+++ b/plugins/axiomcode/skills/axiomcode/scripts/ax_fresh.py
@@ -64,6 +64,17 @@
     'python': ('pyproject.toml', 'setup.cfg', 'setup.py'),
     'csharp': ('global.json', 'Directory.Build.props'),
 }
+# EXTENSION CASE (#1771). The JavaScript parser matches an extension whatever its case (jsExtensionOf lower-cases the
+# name, so Main.JS and Up.VUE are read) and the C# parser reads *.CS (discoverCsFiles); the others match it exactly.
+# Matched exactly here, such a file was parsed but left out of the table: an edit to it was invisible and `index` said
+# "graph up to date". These are the extensions each parser folds; every other one stays case-sensitive, as its parser is.
+FOLD = {'javascript': frozenset(EXT['javascript']), 'csharp': frozenset({'.cs'})}
+
+def has_ext(lang, name, exts):
+    """True when the parser of `lang` takes file `name` as ending in one of `exts`"""
+    if name.endswith(exts): return True
+    fold = FOLD.get(lang)
+    return bool(fold) and name.lower().endswith(tuple(e for e in exts if e in fold))
 # TOOL OUTPUT NOBODY PARSES: what the non-source scan of `impact` (axiomcode-impact) leaves out. NOT what the file table
 # prunes: that is SKIP below, per language.
 PRUNE_ALL = {'.git', '.hg', '.svn', '.axiomcode', 'node_modules', 'bower_components', 'dist', 'build', 'out',
@@ -194,7 +205,7 @@ def watched(root, lang):
         for f in files:
             for l, exts, names in spec:
                 if l in off: continue
-                if f.endswith(exts) or f in names or (l == 'java' and os.path.basename(d) == 'services' and 'META-INF' in d) \
+                if has_ext(l, f, exts) or f in names or (l == 'java' and os.path.basename(d) == 'services' and 'META-INF' in d) \
                         or (l == 'python' and python_script(os.path.join(d, f), f)):
                     yield os.path.join(d, f); break
 
@@ -1118,7 +1129,7 @@ def main(argv):
         n = {l: 0 for l in SOURCE}
         for l in SOURCE:
             for p in watched(repo, l):
-                if p.endswith(SOURCE[l]) or (l == 'python' and python_script(p)): n[l] += 1
+                if has_ext(l, os.path.basename(p), SOURCE[l]) or (l == 'python' and python_script(p)): n[l] += 1
         print(n['java'], n['typescript'], n['python'], n['javascript'], n['csharp']); return 0
     if cmd == 'pyscripts':
         # how many extensionless python scripts are under repo: added to the build's .py count when it picks a language
diff --git a/tests/freshness.py b/tests/freshness.py
index 97ffa425f..47242267b 100644
--- a/tests/freshness.py
+++ b/tests/freshness.py
@@ -131,6 +131,27 @@ def prune_checks():
         write(only, 'src/App.vue', '<script>export default {}</script>\n')
         n = {l: sum(1 for p in ax_fresh.watched(only, l) if p.endswith(ax_fresh.SOURCE[l])) for l in ('javascript', 'typescript')}
         check("prune: a repository of .vue files alone counts no JavaScript or TypeScript source", n == {'javascript': 0, 'typescript': 0}, n)
+        # EXTENSION CASE (#1771): the JavaScript parser reads Main.JS and Up.VUE and the C# parser reads Calc.CS, so an edit
+        # to one makes the graph stale and they count as source. The control: the TypeScript, Python and Java parsers match
+        # an extension exactly, so Main.TS, calc.PY and Calc.JAVA stay unwatched and uncounted
+        upper = os.path.join(work, 'upper')
+        for f in ('src/lib.js', 'src/Main.JS', 'src/views/Up.VUE', 'src/Old.Mjs', 'src/Main.TS', 'src/calc.PY',
+                  'src/Calc.JAVA', 'src/Calc.CS'):
+            write(upper, f, 'x\n')
+        want = {'javascript': {'src/lib.js', 'src/Main.JS', 'src/views/Up.VUE', 'src/Old.Mjs'}, 'typescript': {'src/lib.js'},
+                'python': set(), 'java': set(), 'csharp': {'src/Calc.CS'}}
+        for lang, files in want.items():
+            got = {os.path.relpath(p, upper) for p in ax_fresh.watched(upper, lang)}
+            check(f"prune: {lang} watches an upper-case extension exactly when its parser reads one", got == files, sorted(got))
+        table = dict(lang='javascript', lang_auto=True, src='', files=ax_fresh.snapshot(upper, 'javascript', upper))
+        write(upper, 'src/Main.JS', 'third();\n'); write(upper, 'src/views/Up.VUE', 'third();\n'); write(upper, 'src/Main.TS', 'y\n')
+        c = ax_fresh.changes(upper, table)
+        check("prune: javascript: an edit to Main.JS or Up.VUE makes the graph stale; one to Main.TS does not",
+              c == (['src/Main.JS', 'src/views/Up.VUE'], [], []), c)
+        n = {l: sum(1 for p in ax_fresh.watched(upper, l) if ax_fresh.has_ext(l, os.path.basename(p), ax_fresh.SOURCE[l]))
+             for l in ax_fresh.SOURCE}
+        check("prune: Main.JS and Calc.CS count as source; Main.TS, calc.PY, Calc.JAVA and Up.VUE do not",
+              n == {'java': 0, 'typescript': 0, 'python': 0, 'javascript': 3, 'csharp': 1}, n)
     finally:
         shutil.rmtree(work, ignore_errors=True)