diff --git a/src/iso19111/io.cpp b/src/iso19111/io.cpp
index d7fcea4933..d9a69849ed 100644
--- a/src/iso19111/io.cpp
+++ b/src/iso19111/io.cpp
@@ -10365,7 +10365,7 @@ PROJStringParser::Private::buildDatum(Step &step, const std::string &title) {
                 return GeodeticReferenceFrame::create(
                     grfMap.set(IdentifiedObject::NAME_KEY,
                                title.empty()
-                                   ? "Unknown based on WGS84 ellipsoid" +
+                                   ? "Unknown based on WGS 84 ellipsoid" +
                                          datumNameSuffix
                                    : title),
                     Ellipsoid::WGS84, optionalEmptyString, pm);
@@ -10373,7 +10373,7 @@ PROJStringParser::Private::buildDatum(Step &step, const std::string &title) {
                 return GeodeticReferenceFrame::create(
                     grfMap.set(IdentifiedObject::NAME_KEY,
                                title.empty()
-                                   ? "Unknown based on GRS80 ellipsoid" +
+                                   ? "Unknown based on GRS 1980 ellipsoid" +
                                          datumNameSuffix
                                    : title),
                     Ellipsoid::GRS1980, optionalEmptyString, pm);
@@ -10441,10 +10441,20 @@ PROJStringParser::Private::buildDatum(Step &step, const std::string &title) {
     const auto createGRF = [&grfMap, &title, &optionalEmptyString,
                             &datumNameSuffix,
                             &pm](const EllipsoidNNPtr &ellipsoid) {
+        std::string datumName(title);
+        if (title.empty()) {
+            if (ellipsoid->nameStr() != "unknown") {
+                datumName = "Unknown based on ";
+                datumName += ellipsoid->nameStr();
+                datumName += " ellipsoid";
+            } else {
+                datumName = "unknown";
+            }
+            datumName += datumNameSuffix;
+        }
         return GeodeticReferenceFrame::create(
-            grfMap.set(IdentifiedObject::NAME_KEY,
-                       title.empty() ? "unknown" + datumNameSuffix : title),
-            ellipsoid, optionalEmptyString, fixupPrimeMeridan(ellipsoid, pm));
+            grfMap.set(IdentifiedObject::NAME_KEY, datumName), ellipsoid,
+            optionalEmptyString, fixupPrimeMeridan(ellipsoid, pm));
     };
 
     if (a > 0 && (b > 0 || !bStr.empty())) {
diff --git a/test/unit/test_io.cpp b/test/unit/test_io.cpp
index 2d8626e29b..bcc3d4ee30 100644
--- a/test/unit/test_io.cpp
+++ b/test/unit/test_io.cpp
@@ -9656,7 +9656,7 @@ TEST(io, projparse_longlat_ellps_WGS84) {
     f->simulCurNodeHasId();
     crs->exportToWKT(f.get());
     auto expected = "GEODCRS[\"unknown\",\n"
-                    "    DATUM[\"Unknown based on WGS84 ellipsoid\",\n"
+                    "    DATUM[\"Unknown based on WGS 84 ellipsoid\",\n"
                     "        ELLIPSOID[\"WGS 84\",6378137,298.257223563,\n"
                     "            LENGTHUNIT[\"metre\",1]]],\n"
                     "    PRIMEM[\"Greenwich\",0,\n"
@@ -9682,7 +9682,7 @@ TEST(io, projparse_longlat_ellps_GRS80) {
     f->simulCurNodeHasId();
     crs->exportToWKT(f.get());
     auto expected = "GEODCRS[\"unknown\",\n"
-                    "    DATUM[\"Unknown based on GRS80 ellipsoid\",\n"
+                    "    DATUM[\"Unknown based on GRS 1980 ellipsoid\",\n"
                     "        ELLIPSOID[\"GRS 1980\",6378137,298.257222101,\n"
                     "            LENGTHUNIT[\"metre\",1]]],\n"
                     "    PRIMEM[\"Greenwich\",0,\n"
@@ -9735,7 +9735,7 @@ TEST(io, projparse_longlat_a_rf_WGS84) {
     f->simulCurNodeHasId();
     crs->exportToWKT(f.get());
     auto expected = "GEODCRS[\"unknown\",\n"
-                    "    DATUM[\"unknown\",\n"
+                    "    DATUM[\"Unknown based on WGS 84 ellipsoid\",\n"
                     "        ELLIPSOID[\"WGS 84\",6378137,298.257223563,\n"
                     "            LENGTHUNIT[\"metre\",1]]],\n"
                     "    PRIMEM[\"Greenwich\",0,\n"
@@ -11621,7 +11621,7 @@ TEST(io, projparse_geocent) {
     f->setMultiLine(false);
     crs->exportToWKT(f.get());
     auto wkt = f->toString();
-    EXPECT_EQ(wkt, "GEODCRS[\"unknown\",DATUM[\"Unknown based on WGS84 "
+    EXPECT_EQ(wkt, "GEODCRS[\"unknown\",DATUM[\"Unknown based on WGS 84 "
                    "ellipsoid\",ELLIPSOID[\"WGS "
                    "84\",6378137,298.257223563,LENGTHUNIT[\"metre\",1]]],"
                    "PRIMEM[\"Greenwich\",0,ANGLEUNIT[\"degree\",0."