diff --git a/src/lib/measurements/__tests__/hk-units.test.ts b/src/lib/measurements/__tests__/hk-units.test.ts
index b1162fb6b..d03b77939 100644
--- a/src/lib/measurements/__tests__/hk-units.test.ts
+++ b/src/lib/measurements/__tests__/hk-units.test.ts
@@ -30,6 +30,8 @@ describe("convertHkValue", () => {
       99.0858,
       4,
     );
+    expect(isConvertibleHkUnit("mmol<180>/L")).toBe(true);
+    expect(isConvertibleHkUnit("mmol<x>/L")).toBe(false);
   });
 
   it("keeps the small calorie apart from the large one", () => {
diff --git a/src/lib/measurements/hk-units.ts b/src/lib/measurements/hk-units.ts
index f500be22d..1b5201b4c 100644
--- a/src/lib/measurements/hk-units.ts
+++ b/src/lib/measurements/hk-units.ts
@@ -120,10 +120,12 @@ const HK_UNITS: Record<string, HkUnitSpec> = {
 
 /**
  * Apple writes molar units with the substance's molar mass inline —
- * `mmol<180.156>/L` for blood glucose. The annotation is informational;
- * strip it so the lookup sees the plain unit.
+ * `mmol<180.156>/L` for blood glucose. The annotation is a number and
+ * informational; strip exactly that shape so the lookup sees the plain
+ * unit. Anything else between angle brackets is not a unit Apple writes
+ * and stays unknown.
  */
-const MOLAR_MASS_ANNOTATION = /<[^>]*>/g;
+const MOLAR_MASS_ANNOTATION = /<\d+(?:\.\d+)?>/g;
 
 function normaliseUnitString(unit: string): string {
   return unit.trim().replace(MOLAR_MASS_ANNOTATION, "");