diff --git a/src/core/cff_parser.js b/src/core/cff_parser.js
index 9fbd85305..2a78c79e5 100644
--- a/src/core/cff_parser.js
+++ b/src/core/cff_parser.js
@@ -902,10 +902,14 @@ class CFFParser {
         // BlueScale up only misaligns/collapses overshooting glyphs (notably
         // with macOS's Core Text rasterizer). Only apply the lower clamp when
         // its target does not exceed the default.
+        // Round the bound in order to avoid too long operand (issue 21466).
+        const PRECISION = 1e5;
         const lowerBound = 0.5 / maxZoneHeight;
         const minBlueScale =
-          lowerBound <= DEFAULT_BLUE_SCALE ? lowerBound : -Infinity;
-        const maxBlueScale = 1 / maxZoneHeight;
+          lowerBound <= DEFAULT_BLUE_SCALE
+            ? Math.ceil(lowerBound * PRECISION) / PRECISION
+            : -Infinity;
+        const maxBlueScale = Math.floor(PRECISION / maxZoneHeight) / PRECISION;
         const clamped = MathClamp(blueScale, minBlueScale, maxBlueScale);
         if (clamped !== blueScale) {
           privateDict.setByName("BlueScale", clamped);
diff --git a/test/unit/cff_parser_spec.js b/test/unit/cff_parser_spec.js
index 80ee917d5..f368d5fa8 100644
--- a/test/unit/cff_parser_spec.js
+++ b/test/unit/cff_parser_spec.js
@@ -389,6 +389,29 @@ describe("CFFParser", function () {
     );
   });
 
+  it("clamps BlueScale to a short decimal so the recompiled operand stays compact", function () {
+    // maxZoneHeight = 13 gives lower bound (0.5 / 13 = 0.038461538461538464)
+    // which is too long (issue 21466).
+    cff.topDict.privateDict = new CFFPrivateDict(cff.strings);
+    cff.topDict.privateDict.setByName(
+      "BlueValues",
+      [-13, 13, 530, 13, 220, 13, 30, 13]
+    );
+    cff.topDict.privateDict.setByName("BlueScale", 0.01);
+    cff.topDict.setByName("Private", [0, 0]);
+    const fontDataShortBlueScale = new CFFCompiler(cff).compile();
+
+    const reparsedCff = new CFFParser(
+      new Stream(fontDataShortBlueScale),
+      {},
+      SEAC_ANALYSIS_ENABLED
+    ).parse();
+
+    const blueScale = reparsedCff.topDict.privateDict.getByName("BlueScale");
+    expect(blueScale).toEqual(0.03847);
+    expect(new CFFCompiler(cff).encodeFloat(blueScale).length).toBeLessThan(6);
+  });
+
   it("refuses to add topDict key with invalid value (bug 1068432)", function () {
     const topDict = cff.topDict;
     const defaultValue = topDict.getByName("UnderlinePosition");