diff --git a/packages/tide-predictor/src/constituents/MP1.ts b/packages/tide-predictor/src/constituents/MP1.ts
new file mode 100644
index 0000000..f6ef8e0
--- /dev/null
+++ b/packages/tide-predictor/src/constituents/MP1.ts
@@ -0,0 +1,14 @@
+import { defineCompoundConstituent } from "./definition.js";
+import M2 from "./M2.js";
+import P1 from "./P1.js";
+
+/**
+ * Solar-lunar diurnal (MP1 = M2 - P1).
+ * Combined solar and lunar diurnal constituent from solar-lunar interaction.
+ * Amplitude typically small; usually <5% of K1.
+ * Rarely significant except in specialized harmonic analyses.
+ */
+export default defineCompoundConstituent("MP1", [
+  { constituent: M2, factor: 1 },
+  { constituent: P1, factor: -1 },
+]);
diff --git a/packages/tide-predictor/test/constituents/index.test.ts b/packages/tide-predictor/test/constituents/index.test.ts
index 47e4780..3028677 100644
--- a/packages/tide-predictor/test/constituents/index.test.ts
+++ b/packages/tide-predictor/test/constituents/index.test.ts
@@ -145,4 +145,9 @@ describe("Base constituent definitions", () => {
     expect(constituents["2MO5"]).toBeDefined();
     expect(constituents["2MO5"].speed(testAstro)).toBeCloseTo(71.911244, 6);
   });
+
+  it("has correct properties for MP1 (solar-lunar diurnal)", () => {
+    expect(constituents.MP1).toBeDefined();
+    expect(constituents.MP1.speed(testAstro)).toBeCloseTo(14.0251729, 7);
+  });
 });