diff --git a/mod.js b/mod.js
index be6b3825..a584ee19 100644
--- a/mod.js
+++ b/mod.js
@@ -745,6 +745,10 @@ function analogous(color, results, slices) {
   results = results || 6;
   slices = slices || 30;
 
+  if (isNaN(results) || results <= 0 || results % 1 !== 0) {
+    throw new Error("Argument to analogous must be a positive integer");
+  }
+
   var hsl = tinycolor(color).toHsl();
   var part = 360 / slices;
   var ret = [tinycolor(color)];
@@ -758,6 +762,10 @@ function analogous(color, results, slices) {
 
 function monochromatic(color, results) {
   results = results || 6;
+
+  if (isNaN(results) || results <= 0 || results % 1 !== 0) {
+    throw new Error("Argument to monochromatic must be a positive integer");
+  }
   var hsv = tinycolor(color).toHsv();
   var h = hsv.h,
     s = hsv.s,
diff --git a/npm/cjs/tinycolor.js b/npm/cjs/tinycolor.js
index 4f584cab..8ef99ea5 100644
--- a/npm/cjs/tinycolor.js
+++ b/npm/cjs/tinycolor.js
@@ -653,6 +653,10 @@
   function _analogous(color, results, slices) {
     results = results || 6;
     slices = slices || 30;
+
+    if (isNaN(results) || results <= 0 || results % 1 !== 0) {
+      throw new Error("Argument to analogous must be a positive integer");
+    }
     var hsl = tinycolor(color).toHsl();
     var part = 360 / slices;
     var ret = [tinycolor(color)];
@@ -664,6 +668,10 @@
   }
   function _monochromatic(color, results) {
     results = results || 6;
+
+    if (isNaN(results) || results <= 0 || results % 1 !== 0) {
+      throw new Error("Argument to monochromatic must be a positive integer");
+    }
     var hsv = tinycolor(color).toHsv();
     var h = hsv.h,
       s = hsv.s,
diff --git a/npm/esm/tinycolor.js b/npm/esm/tinycolor.js
index 374f5ea9..d00a9e41 100644
--- a/npm/esm/tinycolor.js
+++ b/npm/esm/tinycolor.js
@@ -647,6 +647,10 @@ function _splitcomplement(color) {
 function _analogous(color, results, slices) {
   results = results || 6;
   slices = slices || 30;
+
+  if (isNaN(results) || results <= 0 || results % 1 !== 0) {
+    throw new Error("Argument to analogous must be a positive integer");
+  }
   var hsl = tinycolor(color).toHsl();
   var part = 360 / slices;
   var ret = [tinycolor(color)];
@@ -658,6 +662,10 @@ function _analogous(color, results, slices) {
 }
 function _monochromatic(color, results) {
   results = results || 6;
+
+  if (isNaN(results) || results <= 0 || results % 1 !== 0) {
+    throw new Error("Argument to monochromatic must be a positive integer");
+  }
   var hsv = tinycolor(color).toHsv();
   var h = hsv.h,
     s = hsv.s,
diff --git a/test.js b/test.js
index d6003428..5c6e7cd0 100644
--- a/test.js
+++ b/test.js
@@ -2138,6 +2138,26 @@ Deno.test("tetrad", function () {
   );
 });
 
+Deno.test("analogous and monochromatic reject counts that never terminate", function () {
+  // `--results` / `results--` test for truthiness, so a negative or fractional
+  // count never lands on 0 and the loop allocates until the heap is gone.
+  // `polyad` already guards the same shape of input.
+  for (const bad of [-1, 1.5, 0.5, -0.5]) {
+    assertThrows(() => {
+      tinycolor("red").analogous(bad);
+    });
+    assertThrows(() => {
+      tinycolor("red").monochromatic(bad);
+    });
+  }
+
+  // Falsy values still fall through to the default of 6, unchanged.
+  assertEquals(tinycolor("red").analogous().length, 6);
+  assertEquals(tinycolor("red").analogous(0).length, 6);
+  assertEquals(tinycolor("red").monochromatic(null).length, 6);
+  assertEquals(tinycolor("red").analogous(3).length, 3);
+});
+
 Deno.test({
   name: "polyad",
   // Disabled until https://github.com/bgrins/TinyColor/issues/254
diff --git a/tinycolor.js b/tinycolor.js
index e52a3d55..25daf20a 100644
--- a/tinycolor.js
+++ b/tinycolor.js
@@ -652,6 +652,10 @@
   function _analogous(color, results, slices) {
     results = results || 6;
     slices = slices || 30;
+
+    if (isNaN(results) || results <= 0 || results % 1 !== 0) {
+      throw new Error("Argument to analogous must be a positive integer");
+    }
     var hsl = tinycolor(color).toHsl();
     var part = 360 / slices;
     var ret = [tinycolor(color)];
@@ -663,6 +667,10 @@
   }
   function _monochromatic(color, results) {
     results = results || 6;
+
+    if (isNaN(results) || results <= 0 || results % 1 !== 0) {
+      throw new Error("Argument to monochromatic must be a positive integer");
+    }
     var hsv = tinycolor(color).toHsv();
     var h = hsv.h,
       s = hsv.s,