diff --git a/docs/changelog.md b/docs/changelog.md
index 3ad1b31a..a4835faf 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -52,6 +52,9 @@ Requires libvips v8.13.0
   Emit warnings when previous calls in the same pipeline will be ignored.
   [#3319](https://github.com/lovell/sharp/issues/3319)
 
+* Ensure PNG bitdepth can be set for non-palette output.
+  [#3322](https://github.com/lovell/sharp/issues/3322)
+
 * Ensure resized image is unpremultiplied before composite.
   [#3334](https://github.com/lovell/sharp/issues/3334)
 
diff --git a/lib/output.js b/lib/output.js
index dcdfbb02..338c9a04 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -407,6 +407,14 @@ function png (options) {
     if (is.defined(options.adaptiveFiltering)) {
       this._setBooleanOption('pngAdaptiveFiltering', options.adaptiveFiltering);
     }
+    const colours = options.colours || options.colors;
+    if (is.defined(colours)) {
+      if (is.integer(colours) && is.inRange(colours, 2, 256)) {
+        this.options.pngBitdepth = bitdepthFromColourCount(colours);
+      } else {
+        throw is.invalidParameterError('colours', 'integer between 2 and 256', colours);
+      }
+    }
     if (is.defined(options.palette)) {
       this._setBooleanOption('pngPalette', options.palette);
     } else if ([options.quality, options.effort, options.colours, options.colors, options.dither].some(is.defined)) {
@@ -427,14 +435,6 @@ function png (options) {
           throw is.invalidParameterError('effort', 'integer between 1 and 10', options.effort);
         }
       }
-      const colours = options.colours || options.colors;
-      if (is.defined(colours)) {
-        if (is.integer(colours) && is.inRange(colours, 2, 256)) {
-          this.options.pngBitdepth = bitdepthFromColourCount(colours);
-        } else {
-          throw is.invalidParameterError('colours', 'integer between 2 and 256', colours);
-        }
-      }
       if (is.defined(options.dither)) {
         if (is.number(options.dither) && is.inRange(options.dither, 0, 1)) {
           this.options.pngDither = options.dither;
diff --git a/test/unit/png.js b/test/unit/png.js
index e996b514..b3bf4fc1 100644
--- a/test/unit/png.js
+++ b/test/unit/png.js
@@ -190,6 +190,23 @@ describe('PNG', function () {
     });
   });
 
+  it('Can set bitdepth of PNG without palette', async () => {
+    const data = await sharp({
+      create: {
+        width: 8, height: 8, channels: 3, background: 'red'
+      }
+    })
+      .toColourspace('b-w')
+      .png({ colours: 2, palette: false })
+      .toBuffer();
+
+    const { channels, paletteBitDepth, size, space } = await sharp(data).metadata();
+    assert.strictEqual(channels, 1);
+    assert.strictEqual(paletteBitDepth, undefined);
+    assert.strictEqual(size, 90);
+    assert.strictEqual(space, 'b-w');
+  });
+
   it('Valid PNG libimagequant dither value produces image of same size or smaller', function () {
     const inputPngBuffer = fs.readFileSync(fixtures.inputPng);
     return Promise.all([