diff --git a/fixtures/geotiff-test-data b/fixtures/geotiff-test-data
index 7fa07ac1..6f403786 160000
--- a/fixtures/geotiff-test-data
+++ b/fixtures/geotiff-test-data
@@ -1 +1 @@
-Subproject commit 7fa07ac10f9d54b2ac2e557117432cf8f2f80eef
+Subproject commit 6f4037861ed474d39ef81d02207b3f252c897d7d
diff --git a/packages/geotiff/src/array.ts b/packages/geotiff/src/array.ts
index a0417089..b25be9c7 100644
--- a/packages/geotiff/src/array.ts
+++ b/packages/geotiff/src/array.ts
@@ -43,8 +43,13 @@ export type RasterArrayBase = {
    */
   transform: Affine;
 
-  /** Coordinate reference system information. */
-  crs: number | ProjJson;
+  /** Coordinate reference system information.
+   *
+   * - If `crs` is a number, it is an EPSG code.
+   * - If `crs` is an object, it is a PROJJSON object.
+   * - If `crs` is a string, it is an ESRI WKT (this is rare).
+   */
+  crs: number | ProjJson | string;
 
   /** Nodata value from `GDAL_NODATA` TIFF tag. */
   nodata: number | null;
diff --git a/packages/geotiff/src/crs.ts b/packages/geotiff/src/crs.ts
index a535edfc..6dce837c 100644
--- a/packages/geotiff/src/crs.ts
+++ b/packages/geotiff/src/crs.ts
@@ -74,10 +74,13 @@ const LINEAR_UNIT: Record<number, string | ProjJsonUnit> = {
  * Parse a CRS from a GeoKeyDirectory.
  *
  * Returns the EPSG code as a number for EPSG-coded CRSes (letting the caller
- * decide how to resolve it), or a PROJJSON object built from the geo keys for
- * user-defined CRSes.
+ * decide how to resolve it), a PROJJSON object built from the geo keys for
+ * user-defined CRSes, or a raw WKT string when the GeoTIFF carries an
+ * `ESRI PE String = ...` citation under a fully user-defined model type.
  */
-export function crsFromGeoKeys(gkd: GeoKeyDirectory): number | ProjJson {
+export function crsFromGeoKeys(
+  gkd: GeoKeyDirectory,
+): number | ProjJson | string {
   const modelType = gkd.modelType;
 
   if (modelType === MODEL_TYPE_PROJECTED) {
@@ -88,7 +91,35 @@ export function crsFromGeoKeys(gkd: GeoKeyDirectory): number | ProjJson {
     return _geographicCrs(gkd);
   }
 
-  throw new Error(`Unsupported GeoTIFF model type: ${modelType}`);
+  if (modelType === USER_DEFINED) {
+    const wkt = _esriPeString(gkd);
+    if (wkt !== null) {
+      return wkt;
+    }
+  }
+
+  throw new Error(
+    `Unsupported GeoTIFF CRS definition with model type: ${modelType}`,
+  );
+}
+
+const ESRI_PE_STRING_PREFIX = "ESRI PE String =";
+
+/**
+ * Extract a WKT string from an `ESRI PE String = ...` ProjectedCitation.
+ *
+ * The GeoTIFF spec defines no text-based CRS encoding; `ESRI PE String =` is
+ * a de facto ArcGIS convention that GDAL/PROJ also read. It is used when the
+ * model type itself is user-defined (32767) and no projection method/parameter
+ * geo keys are present — the WKT in the citation is then the only CRS signal.
+ */
+function _esriPeString(gkd: GeoKeyDirectory): string | null {
+  const citation = gkd.projectedCitation;
+  if (citation === null || !citation.includes(ESRI_PE_STRING_PREFIX)) {
+    return null;
+  }
+  const wkt = citation.split(ESRI_PE_STRING_PREFIX, 2)[1]?.trim();
+  return wkt ? wkt : null;
 }
 
 function _geographicCrs(gkd: GeoKeyDirectory): number | GeographicCRS {
diff --git a/packages/geotiff/src/fetch.ts b/packages/geotiff/src/fetch.ts
index 299abc2d..11492ee2 100644
--- a/packages/geotiff/src/fetch.ts
+++ b/packages/geotiff/src/fetch.ts
@@ -25,7 +25,7 @@ interface HasTiffReference extends HasTransform {
   readonly maskImage: TiffImage | null;
 
   /** The coordinate reference system. */
-  readonly crs: number | ProjJson;
+  readonly crs: number | ProjJson | string;
 
   /** The height of tiles in pixels. */
   readonly tileHeight: number;
diff --git a/packages/geotiff/src/geotiff.ts b/packages/geotiff/src/geotiff.ts
index f23b0a17..62687c66 100644
--- a/packages/geotiff/src/geotiff.ts
+++ b/packages/geotiff/src/geotiff.ts
@@ -73,7 +73,7 @@ export class GeoTIFF {
   readonly overviews: Overview[];
 
   /** A cached CRS value. */
-  private _crs?: number | ProjJson;
+  private _crs?: number | ProjJson | string;
 
   /** Cached TIFF tags that are pre-fetched when opening the GeoTIFF. */
   readonly cachedTags: CachedTags;
@@ -361,15 +361,15 @@ export class GeoTIFF {
 
   // ── Properties from the primary image ─────────────────────────────────
 
-  /**
-   * The CRS parsed from the GeoKeyDirectory.
+  /** Coordinate reference system information.
    *
-   * Returns an EPSG code (number) for EPSG-coded CRSes, or a PROJJSON object
-   * for user-defined CRSes. The result is cached after the first access.
+   * - If `crs` is a number, it is an EPSG code.
+   * - If `crs` is an object, it is a PROJJSON object.
+   * - If `crs` is a string, it is an ESRI WKT (this is rare).
    *
-   * See also {@link GeoTIFF.epsg} for the EPSG code directly from the TIFF tags.
+   * The result is cached after the first access.
    */
-  get crs(): number | ProjJson {
+  get crs(): number | ProjJson | string {
     if (this._crs === undefined) {
       this._crs = crsFromGeoKeys(this.gkd);
     }
diff --git a/packages/geotiff/src/overview.ts b/packages/geotiff/src/overview.ts
index 8af8c306..bd681ddb 100644
--- a/packages/geotiff/src/overview.ts
+++ b/packages/geotiff/src/overview.ts
@@ -48,15 +48,15 @@ export class Overview {
     this.dataSource = dataSource;
   }
 
-  /**
-   * The CRS parsed from the GeoKeyDirectory.
+  /** Coordinate reference system information.
    *
-   * Returns an EPSG code (number) for EPSG-coded CRSes, or a PROJJSON object
-   * for user-defined CRSes. The result is cached after the first access.
+   * - If `crs` is a number, it is an EPSG code.
+   * - If `crs` is an object, it is a PROJJSON object.
+   * - If `crs` is a string, it is an ESRI WKT (this is rare).
    *
-   * See also {@link GeoTIFF.epsg} for the EPSG code directly from the TIFF tags.
+   * The result is cached after the first access.
    */
-  get crs(): number | ProjJson {
+  get crs(): number | ProjJson | string {
     return this.geotiff.crs;
   }
 
diff --git a/packages/geotiff/src/tile-matrix-set.ts b/packages/geotiff/src/tile-matrix-set.ts
index 9139f116..b5ee86a3 100644
--- a/packages/geotiff/src/tile-matrix-set.ts
+++ b/packages/geotiff/src/tile-matrix-set.ts
@@ -29,13 +29,19 @@ interface ProjectionDefinition {
 
 const SCREEN_PIXEL_SIZE = 0.28e-3;
 
-function buildCrs(crs: number | ProjJson): CRS {
+function buildCrs(crs: number | ProjJson | string): CRS {
   if (typeof crs === "number") {
     return {
       uri: `http://www.opengis.net/def/crs/EPSG/0/${crs}`,
     };
   }
 
+  // Raw WKT string (e.g. from an ESRI PE String citation) — the OGC TMS CRS
+  // type allows a bare string form.
+  if (typeof crs === "string") {
+    return crs;
+  }
+
   // @ts-expect-error - typing issues between different projjson definitions.
   return {
     wkt: crs,
diff --git a/packages/geotiff/tests/crs.test.ts b/packages/geotiff/tests/crs.test.ts
index b9402b83..bc322d21 100644
--- a/packages/geotiff/tests/crs.test.ts
+++ b/packages/geotiff/tests/crs.test.ts
@@ -108,4 +108,26 @@ describe("test GeoKey CRS parsing", () => {
     expect(proj.units).toBe("meter");
     expect(proj.projName).toBe("Albers Equal Area");
   });
+
+  it("can parse an ESRI PE String citation under a user-defined model type", async () => {
+    // hfp_2017_100m_v1-2_cog: GTModelTypeGeoKey = 32767 (ModelTypeUserDefined),
+    // CRS only reconstructable from the `ESRI PE String = ...` citation.
+    const geotiff = await loadGeoTIFF(
+      "hfp_2017_100m_v1-2_cog",
+      "source-coop-vizzuality",
+    );
+    const crs = geotiff.crs;
+
+    if (typeof crs !== "string") {
+      throw new Error("expected raw WKT string for ESRI PE String CRS");
+    }
+    expect(crs.startsWith("PROJCS[")).toBe(true);
+    expect(crs).toContain("Mollweide");
+
+    // wkt-parser must be able to consume the WKT for downstream TMS use.
+    const proj = parseWkt(crs);
+    expect(proj.projName).toBe("Mollweide");
+    expect(proj.units).toBe("meter");
+    expect(proj.a ?? proj.datum?.a).toBe(6378137);
+  });
 });