diff --git a/Sources/LoopAlgorithm/LoopUnit.swift b/Sources/LoopAlgorithm/LoopUnit.swift
index a97f965..370334b 100644
--- a/Sources/LoopAlgorithm/LoopUnit.swift
+++ b/Sources/LoopAlgorithm/LoopUnit.swift
@@ -73,18 +73,19 @@ public enum LoopUnit: Sendable, CaseIterable {
              (.milligramsPerDeciliterPerInternationalUnit, .millimolesPerLiterPerInternationalUnit):
             return 1/UnitMolarMassBloodGlucoseDivisible
         case (.milligramsPerDeciliterPerSecond, .millimolesPerLiterPerMinute):
-            return 1/UnitMolarMassBloodGlucoseDivisible / 60
-        case (.milligramsPerDeciliterPerMinute, .millimolesPerLiterPerSecond):
+            // Rate: per-second -> per-minute multiplies by 60 (opposite of a duration conversion)
             return 1/UnitMolarMassBloodGlucoseDivisible * 60
+        case (.milligramsPerDeciliterPerMinute, .millimolesPerLiterPerSecond):
+            return 1/UnitMolarMassBloodGlucoseDivisible / 60
         case (.millimolesPerLiter, .milligramsPerDeciliter),
              (.millimolesPerLiterPerSecond, .milligramsPerDeciliterPerSecond),
              (.millimolesPerLiterPerMinute, .milligramsPerDeciliterPerMinute),
              (.millimolesPerLiterPerInternationalUnit, .milligramsPerDeciliterPerInternationalUnit):
             return UnitMolarMassBloodGlucoseDivisible
         case (.millimolesPerLiterPerSecond, .milligramsPerDeciliterPerMinute):
-            return UnitMolarMassBloodGlucoseDivisible / 60
-        case (.millimolesPerLiterPerMinute, .milligramsPerDeciliterPerSecond):
             return UnitMolarMassBloodGlucoseDivisible * 60
+        case (.millimolesPerLiterPerMinute, .milligramsPerDeciliterPerSecond):
+            return UnitMolarMassBloodGlucoseDivisible / 60
         case (.gram, _),
              (.gramsPerUnit, _),
              (.internationalUnit, _),
diff --git a/Tests/LoopAlgorithmTests/LoopUnitTests.swift b/Tests/LoopAlgorithmTests/LoopUnitTests.swift
index 94def32..8c78cfe 100644
--- a/Tests/LoopAlgorithmTests/LoopUnitTests.swift
+++ b/Tests/LoopAlgorithmTests/LoopUnitTests.swift
@@ -190,18 +190,45 @@ class LoopUnitTests: XCTestCase {
         
         unit1 = LoopUnit.milligramsPerDeciliterPerMinute
         unit2 = LoopUnit.millimolesPerLiterPerSecond
-        XCTAssertEqual(unit1.conversionFactor(toUnit: unit2), 1/UnitMolarMassBloodGlucoseDivisible * 60)
-        XCTAssertEqual(unit2.conversionFactor(toUnit: unit1), UnitMolarMassBloodGlucoseDivisible / 60)
+        XCTAssertEqual(unit1.conversionFactor(toUnit: unit2), 1/UnitMolarMassBloodGlucoseDivisible / 60)
+        XCTAssertEqual(unit2.conversionFactor(toUnit: unit1), UnitMolarMassBloodGlucoseDivisible * 60)
         
         unit1 = LoopUnit.milligramsPerDeciliterPerSecond
         unit2 = LoopUnit.millimolesPerLiterPerMinute
-        XCTAssertEqual(unit1.conversionFactor(toUnit: unit2), 1/UnitMolarMassBloodGlucoseDivisible / 60)
-        XCTAssertEqual(unit2.conversionFactor(toUnit: unit1), UnitMolarMassBloodGlucoseDivisible * 60)
+        XCTAssertEqual(unit1.conversionFactor(toUnit: unit2), 1/UnitMolarMassBloodGlucoseDivisible * 60)
+        XCTAssertEqual(unit2.conversionFactor(toUnit: unit1), UnitMolarMassBloodGlucoseDivisible / 60)
         
         let quantity1 = LoopQuantity(unit: .millimolesPerLiter, doubleValue: 4)
         let quantity2 = LoopQuantity(unit: .milligramsPerDeciliter, doubleValue: 72.06235200002165)
         XCTAssertEqual(quantity1, quantity2)
     }
+
+    /// The conversion table is maintained by hand, so check every pair against HealthKit,
+    /// which does the dimensional analysis for us. This guards against transcription errors
+    /// like the inverted time factor that made mg/dL·s -> mmol/L·min 3600x too small.
+    func testConversionFactorsMatchHealthKit() {
+        for source in LoopUnit.allCases {
+            for target in LoopUnit.allCases {
+                let context = "\(source.unitString) -> \(target.unitString)"
+                let one = HKQuantity(unit: HKUnit(from: source.unitString), doubleValue: 1)
+                let hkTarget = HKUnit(from: target.unitString)
+                let convertible = one.is(compatibleWith: hkTarget)
+
+                guard let factor = source.conversionFactor(toUnit: target) else {
+                    XCTAssertFalse(convertible, "\(context) is convertible in HealthKit but returned nil")
+                    continue
+                }
+
+                guard convertible else {
+                    XCTFail("\(context) returned a factor but is not convertible in HealthKit")
+                    continue
+                }
+
+                let expected = one.doubleValue(for: hkTarget)
+                XCTAssertEqual(factor, expected, accuracy: max(abs(expected) * 1e-12, .ulpOfOne), context)
+            }
+        }
+    }
 }
 
 extension LoopUnitTests {