diff --git a/ontopy/ontology.py b/ontopy/ontology.py
index 7e8b2958e..ee0887896 100644
--- a/ontopy/ontology.py
+++ b/ontopy/ontology.py
@@ -15,6 +15,7 @@
 from pathlib import Path
 from collections import defaultdict
 from collections.abc import Iterable
+from urllib.request import HTTPError
 
 import rdflib
 from rdflib.util import guess_format
@@ -670,14 +671,32 @@ def getmtime(path):
 
                 self.loaded = False
                 with open(output, "rb") as handle:
-                    return super().load(
-                        only_local=True,
-                        fileobj=handle,
-                        reload=reload,
-                        reload_if_newer=reload_if_newer,
-                        format="rdfxml",
-                        **kwargs,
-                    )
+                    try:
+                        return super().load(
+                            only_local=True,
+                            fileobj=handle,
+                            reload=reload,
+                            reload_if_newer=reload_if_newer,
+                            format="rdfxml",
+                            **kwargs,
+                        )
+                    except HTTPError as exc:  # Add url to HTTPError message
+                        raise HTTPError(
+                            url=exc.url,
+                            code=exc.code,
+                            msg=f"{exc.url}: {exc.msg}",
+                            hdrs=exc.hdrs,
+                            fp=exc.fp,
+                        ).with_traceback(exc.__traceback__)
+
+        except HTTPError as exc:  # Add url to HTTPError message
+            raise HTTPError(
+                url=exc.url,
+                code=exc.code,
+                msg=f"{exc.url}: {exc.msg}",
+                hdrs=exc.hdrs,
+                fp=exc.fp,
+            ).with_traceback(exc.__traceback__)
 
     def save(
         self,
diff --git a/ontopy/utils.py b/ontopy/utils.py
index 9574bbe85..d193973f4 100644
--- a/ontopy/utils.py
+++ b/ontopy/utils.py
@@ -15,6 +15,7 @@
 
 from rdflib import Graph, URIRef
 from rdflib.util import guess_format
+from rdflib.plugin import PluginException
 
 import owlready2
 
@@ -26,9 +27,10 @@
 
 # Format mappings: file extension -> rdflib format name
 FMAP = {
+    "": "turtle",
+    "ttl": "turtle",
     "n3": "ntriples",
     "nt": "ntriples",
-    "ttl": "turtle",
     "owl": "xml",
     "rdfxml": "xml",
 }
@@ -579,7 +581,12 @@ def recur(graph, outext):
         )
 
     graph = Graph()
-    graph.parse(input_ontology, format=fmt)
+    try:
+        graph.parse(input_ontology, format=fmt)
+    except PluginException as exc:  # Add input_ontology to exception msg
+        raise PluginException(
+            f'Cannot load "{input_ontology}": {exc.msg}'
+        ).with_traceback(exc.__traceback__)
     graph.serialize(destination=output_ontology, format=output_format)
     recur(graph, outext)
 
diff --git a/tests/test_load.py b/tests/test_load.py
index c3366f5fb..f1bdadb34 100755
--- a/tests/test_load.py
+++ b/tests/test_load.py
@@ -5,7 +5,10 @@
 
 
 def test_load(repo_dir: "Path", testonto: "Ontology") -> None:
+    import pytest
+
     from ontopy import get_ontology
+    from ontopy.ontology import HTTPError
 
     # Check that the defaults works
     emmo = get_ontology("emmo").load()  # ttl format
@@ -32,6 +35,12 @@ def test_load(repo_dir: "Path", testonto: "Ontology") -> None:
     ).load()
     assert onto.Electrolyte.prefLabel.first() == "Electrolyte"
 
+    with pytest.raises(
+        HTTPError,
+        match="HTTP Error 404: https://emmo.info/non-existing/ontology: Not Found",
+    ):
+        get_ontology("http://emmo.info/non-existing/ontology#").load()
+
 
 def test_load_rdfs() -> None:
     from ontopy import get_ontology