diff --git a/src/ol/proj/Units.js b/src/ol/proj/Units.js
index ecf1f4874a..c8f13c3bed 100644
--- a/src/ol/proj/Units.js
+++ b/src/ol/proj/Units.js
@@ -8,6 +8,11 @@
  * @enum {string}
  */
 const Units = {
+  /**
+   * Radians
+   * @api
+   */
+  RADIANS: 'radians',
   /**
    * Degrees
    * @api
@@ -40,6 +45,26 @@ const Units = {
   USFEET: 'us-ft',
 };
 
+/**
+ * See http://duff.ess.washington.edu/data/raster/drg/docs/geotiff.txt
+ * @type {Object<number, Units>}
+ */
+const unitByCode = {
+  '9001': Units.METERS,
+  '9002': Units.FEET,
+  '9003': Units.USFEET,
+  '9101': Units.RADIANS,
+  '9102': Units.DEGREES,
+};
+
+/**
+ * @param {number} code Unit code.
+ * @return {Units} Units.
+ */
+export function fromCode(code) {
+  return unitByCode[code];
+}
+
 /**
  * Meters per unit lookup table.
  * @const
@@ -48,6 +73,7 @@ const Units = {
  */
 export const METERS_PER_UNIT = {};
 // use the radius of the Normal sphere
+METERS_PER_UNIT[Units.RADIANS] = 6370997 / (2 * Math.PI);
 METERS_PER_UNIT[Units.DEGREES] = (2 * Math.PI * 6370997) / 360;
 METERS_PER_UNIT[Units.FEET] = 0.3048;
 METERS_PER_UNIT[Units.METERS] = 1;
diff --git a/src/ol/source/GeoTIFF.js b/src/ol/source/GeoTIFF.js
index 8abee1a59b..1ee25e94ff 100644
--- a/src/ol/source/GeoTIFF.js
+++ b/src/ol/source/GeoTIFF.js
@@ -5,10 +5,11 @@ import DataTile from './DataTile.js';
 import State from './State.js';
 import TileGrid from '../tilegrid/TileGrid.js';
 import {Pool, fromUrl as tiffFromUrl, fromUrls as tiffFromUrls} from 'geotiff';
+import {Projection, get as getCachedProjection} from '../proj.js';
 import {create as createDecoderWorker} from '../worker/geotiff-decoder.js';
 import {getIntersection} from '../extent.js';
-import {get as getProjection} from '../proj.js';
 import {toSize} from '../size.js';
+import {fromCode as unitsFromCode} from '../proj/Units.js';
 
 /**
  * @typedef {Object} SourceInfo
@@ -25,10 +26,22 @@ import {toSize} from '../size.js';
  * near-infrared band, configure `bands: [4]`.
  */
 
+/**
+ * @typedef {Object} GeoKeys
+ * @property {number} GTModelTypeGeoKey Model type.
+ * @property {number} GTRasterTypeGeoKey Raster type.
+ * @property {number} GeogAngularUnitsGeoKey Angular units.
+ * @property {number} GeogInvFlatteningGeoKey Inverse flattening.
+ * @property {number} GeogSemiMajorAxisGeoKey Semi-major axis.
+ * @property {number} GeographicTypeGeoKey Geographic coordinate system code.
+ * @property {number} ProjLinearUnitsGeoKey Projected linear unit code.
+ * @property {number} ProjectedCSTypeGeoKey Projected coordinate system code.
+ */
+
 /**
  * @typedef {Object} GeoTIFFImage
  * @property {Object} fileDirectory The file directory.
- * @property {Object} geoKeys The parsed geo-keys.
+ * @property {GeoKeys} geoKeys The parsed geo-keys.
  * @property {boolean} littleEndian Uses little endian byte order.
  * @property {Object} tiles The tile cache.
  * @property {boolean} isTiled The image is tiled.
@@ -91,6 +104,49 @@ function getResolution(image, referenceImage) {
   }
 }
 
+/**
+ * @param {GeoTIFFImage} image A GeoTIFF.
+ * @return {import("../proj/Projection.js").default} The image projection.
+ */
+function getProjection(image) {
+  const geoKeys = image.geoKeys;
+  if (!geoKeys) {
+    return null;
+  }
+
+  if (geoKeys.ProjectedCSTypeGeoKey) {
+    const code = 'EPSG:' + geoKeys.ProjectedCSTypeGeoKey;
+    let projection = getCachedProjection(code);
+    if (!projection) {
+      const units = unitsFromCode(geoKeys.ProjLinearUnitsGeoKey);
+      if (units) {
+        projection = new Projection({
+          code: code,
+          units: units,
+        });
+      }
+    }
+    return projection;
+  }
+
+  if (geoKeys.GeographicTypeGeoKey) {
+    const code = 'EPSG:' + geoKeys.GeographicTypeGeoKey;
+    let projection = getCachedProjection(code);
+    if (!projection) {
+      const units = unitsFromCode(geoKeys.GeogAngularUnitsGeoKey);
+      if (units) {
+        projection = new Projection({
+          code: code,
+          units: units,
+        });
+      }
+    }
+    return projection;
+  }
+
+  return null;
+}
+
 /**
  * @param {import("geotiff/src/geotiff.js").GeoTIFF|import("geotiff/src/geotiff.js").MultiGeoTIFF} tiff A GeoTIFF.
  * @return {Promise<Array<import("geotiff/src/geotiffimage.js").GeoTIFFImage>>} Resolves to a list of images.
@@ -419,14 +475,10 @@ class GeoTIFFSource extends DataTile {
       const firstSource = sources[0];
       for (let i = firstSource.length - 1; i >= 0; --i) {
         const image = firstSource[i];
-        if (image.geoKeys) {
-          const code =
-            image.geoKeys.ProjectedCSTypeGeoKey ||
-            image.geoKeys.GeographicTypeGeoKey;
-          if (code) {
-            this.projection = getProjection('EPSG:' + code);
-            break;
-          }
+        const projection = getProjection(image);
+        if (projection) {
+          this.projection = projection;
+          break;
         }
       }
     }
diff --git a/test/browser/spec/ol/source/geotiff.test.js b/test/browser/spec/ol/source/geotiff.test.js
index de76b67e98..80842afeae 100644
--- a/test/browser/spec/ol/source/geotiff.test.js
+++ b/test/browser/spec/ol/source/geotiff.test.js
@@ -2,7 +2,7 @@ import GeoTIFFSource from '../../../../../src/ol/source/GeoTIFF.js';
 import State from '../../../../../src/ol/source/State.js';
 import TileState from '../../../../../src/ol/TileState.js';
 
-describe('ol.source.GeoTIFF', function () {
+describe('ol/source/GeoTIFF', function () {
   /** @type {GeoTIFFSource} */
   let source;
   beforeEach(function () {
@@ -30,6 +30,7 @@ describe('ol.source.GeoTIFF', function () {
       expect(source.nodataValues_).to.eql([[0]]);
       expect(source.getTileGrid().getResolutions().length).to.be(1);
       expect(source.projection.getCode()).to.be('EPSG:4326');
+      expect(source.projection.getUnits()).to.be('degrees');
       done();
     });
   });