diff --git a/src/auto-reply/reply/memory-flush.ts b/src/auto-reply/reply/memory-flush.ts
index 95f6dbaa053..967f1007a0a 100644
--- a/src/auto-reply/reply/memory-flush.ts
+++ b/src/auto-reply/reply/memory-flush.ts
@@ -197,9 +197,12 @@ export function shouldRunMemoryFlush(params: {
     return false;
   }
   const contextWindow = Math.max(1, Math.floor(params.contextWindowTokens));
-  const reserveTokens = Math.max(0, Math.floor(params.reserveTokensFloor));
   const softThreshold = Math.max(0, Math.floor(params.softThresholdTokens));
-  const threshold = Math.max(0, contextWindow - reserveTokens - softThreshold);
+  const reserveTokens = Math.min(
+    Math.max(0, Math.floor(params.reserveTokensFloor)),
+    Math.max(0, contextWindow - softThreshold - 1),
+  );
+  const threshold = contextWindow - reserveTokens - softThreshold;
   if (threshold <= 0) {
     return false;
   }
diff --git a/src/auto-reply/reply/reply-state.test.ts b/src/auto-reply/reply/reply-state.test.ts
index f83d313e2d3..4db8c4c39d3 100644
--- a/src/auto-reply/reply/reply-state.test.ts
+++ b/src/auto-reply/reply/reply-state.test.ts
@@ -357,6 +357,17 @@ describe("shouldRunMemoryFlush", () => {
       }),
     ).toBe(false);
   });
+
+  it("triggers when reserveTokensFloor equals contextWindowTokens", () => {
+    expect(
+      shouldRunMemoryFlush({
+        entry: { totalTokens: 199_000, compactionCount: 0 },
+        contextWindowTokens: 200_000,
+        reserveTokensFloor: 200_000,
+        softThresholdTokens: 4_000,
+      }),
+    ).toBe(true);
+  });
 });
 
 describe("hasAlreadyFlushedForCurrentCompaction", () => {
@@ -483,4 +494,4 @@ describe("incrementCompactionCount", () => {
     // totalTokens unchanged
     expect(stored[sessionKey].totalTokens).toBe(180_000);
   });
-});
+});
\ No newline at end of file