diff --git a/src/__tests__/units/actions/lcms.test.tsx b/src/__tests__/units/actions/lcms.test.tsx
index d1e68c68..35e52b33 100644
--- a/src/__tests__/units/actions/lcms.test.tsx
+++ b/src/__tests__/units/actions/lcms.test.tsx
@@ -15,6 +15,7 @@ import hplcMsTicPosJcamp from "../../fixtures/lc_ms_jcamp_tic_pos";
 import hplcMsTicNegJcamp from "../../fixtures/lc_ms_jcamp_tic_neg";
 import hplcMsUvvisJcamp from "../../fixtures/lc_ms_jcamp_uvvis";
 import lcMsMzChemstationJcamp from "../../fixtures/lc_ms_jcamp_mz_chemstation";
+import msJcamp from "../../fixtures/ms_jcamp";
 
 const hasSpectrumData = (entity: any) => {
   const data = entity?.spectra?.[0]?.data?.[0];
@@ -170,6 +171,20 @@ describe('LCMS ExtractJcamp', () => {
     const pages = extractPages(entity);
     expect(new Set(pages).size).toBeGreaterThan(1);
   });
+
+  it('Extract a plain MS jcamp keeps the MS layout instead of LC/MS', () => {
+    const entity: any = ExtractJcamp(msJcamp);
+    expect(entity.layout).toEqual(LIST_LAYOUT.MS);
+  });
+
+  it('Extract Chemstation MZ still resolves LC/MS when it also carries generic chem-spectra markers', () => {
+    const injected = lcMsMzChemstationJcamp.replace(
+      '##DATA TYPE=MASS SPECTRUM',
+      '##DATA TYPE=MASS SPECTRUM\n##$CSCATEGORY=SPECTRUM\n##$CSSCANAUTOTARGET=1',
+    );
+    const entity: any = ExtractJcamp(injected);
+    expect(entity.layout).toEqual(LIST_LAYOUT.LC_MS);
+  });
 });
 
 describe('LCMS grouping', () => {
diff --git a/src/features/lc-ms/parsing/chemstation.js b/src/features/lc-ms/parsing/chemstation.js
index 806d272c..12d6bb8a 100644
--- a/src/features/lc-ms/parsing/chemstation.js
+++ b/src/features/lc-ms/parsing/chemstation.js
@@ -67,10 +67,9 @@ export const isChemstationLcms = (source, jcamp) => {
   const scanMode = String(info.SCAN_MODE || info.SCANMODE || '').toUpperCase();
   const type = String(info.TYPE || '').toUpperCase();
   const software = String(info.SOFTWARE || '').toUpperCase();
-  const csCategory = jcamp?.info?.$CSCATEGORY;
-  const categories = Array.isArray(csCategory)
-    ? csCategory.map((c) => String(c).toUpperCase())
-    : [];
+  const categories = []
+    .concat(jcamp?.info?.$CSCATEGORY || [])
+    .map((c) => String(c).toUpperCase());
 
   const hasPolarityCategory = categories.some(
     (c) => c.includes('POSITIVE') || c.includes('NEGATIVE') || c.includes('NEUTRAL'),
@@ -123,7 +122,7 @@ export const isChemstationLcms = (source, jcamp) => {
 
   if (
     hasMassSpectrumRootDataType
-    && (hasMassSpectrumDataType || hasScanModeHint || hasTypeHint || hasSoftwareHint)
+    && (hasScanModeHint || hasTypeHint || hasSoftwareHint || hasTicOrUvvisCategory)
   ) {
     return true;
   }
@@ -134,5 +133,15 @@ export const isChemstationLcms = (source, jcamp) => {
     return true;
   }
 
+  // A multi-page MASS SPECTRUM root with no other chromatographic signal is ambiguous:
+  // both a genuine Chemstation m/z export and a plain multi-page MS NTUPLES export look
+  // like this. The only field that reliably tells them apart is this units triplet, which
+  // is unique to the plain export - so it only vetoes this weak fallback, never the
+  // stronger positive evidence handled above.
+  if (hasMassSpectrumRootDataType && hasMultipleSpectra && hasPageMetadata) {
+    const hasMsUnitsTriplet = /##UNITS\s*=\s*M\/Z,\s*RELATIVE ABUNDANCE,\s*SECONDS/i.test(source);
+    return !hasMsUnitsTriplet;
+  }
+
   return false;
 };