diff --git a/annif/backend/svc.py b/annif/backend/svc.py
index e8e1f8617..626f42de3 100644
--- a/annif/backend/svc.py
+++ b/annif/backend/svc.py
@@ -53,7 +53,11 @@ def _corpus_to_texts_and_classes(corpus):
         classes = []
         for doc in corpus.documents:
             texts.append(doc.text)
-            classes.append(doc.uris[0])
+            if len(doc.uris) > 1:
+                raise NotSupportedException(
+                    'SVC backend does not support training on documents ' +
+                    'with multiple subjects.')
+            classes.append(list(doc.uris)[0])
         return texts, classes
 
     def _train_classifier(self, veccorpus, classes):
diff --git a/tests/conftest.py b/tests/conftest.py
index f92e40e92..5e8f1ab45 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -96,6 +96,17 @@ def document_corpus(subject_index):
     return doc_corpus
 
 
+@pytest.fixture(scope='module')
+def document_corpus_single_subject(document_corpus):
+    docs_single_subj = []
+    for doc in document_corpus.documents:
+        uri = list(doc.uris)[0] if len(doc.uris) > 0 else None
+        label = list(doc.labels)[0] if len(doc.labels) > 0 else None
+        docs_single_subj.append(
+            annif.corpus.Document(doc.text, {uri}, {label}))
+    return annif.corpus.DocumentList(docs_single_subj)
+
+
 @pytest.fixture(scope='module')
 def pretrained_vectors():
     return py.path.local(os.path.join(
diff --git a/tests/test_backend_svc.py b/tests/test_backend_svc.py
index 9cc5245d0..df6928ba1 100644
--- a/tests/test_backend_svc.py
+++ b/tests/test_backend_svc.py
@@ -34,26 +34,26 @@ def test_svc_suggest_no_vectorizer(project):
         svc.suggest("example text")
 
 
-def test_svc_train(datadir, document_corpus, project):
+def test_svc_train(datadir, document_corpus_single_subject, project):
     svc_type = annif.backend.get_backend('svc')
     svc = svc_type(
         backend_id='svc',
         config_params={},
         project=project)
 
-    svc.train(document_corpus)
+    svc.train(document_corpus_single_subject)
     assert svc._model is not None
     assert datadir.join('svc-model.gz').exists()
 
 
-def test_svc_train_ngram(datadir, document_corpus, project):
+def test_svc_train_ngram(datadir, document_corpus_single_subject, project):
     svc_type = annif.backend.get_backend('svc')
     svc = svc_type(
         backend_id='svc',
         config_params={'ngram': 2},
         project=project)
 
-    svc.train(document_corpus)
+    svc.train(document_corpus_single_subject)
     assert svc._model is not None
     assert datadir.join('svc-model.gz').exists()
 
@@ -69,6 +69,17 @@ def test_svc_train_cached(datadir, project):
         svc.train("cached")
 
 
+def test_svc_train_multiple_subjects(datadir, document_corpus, project):
+    svc_type = annif.backend.get_backend('svc')
+    svc = svc_type(
+        backend_id='svc',
+        config_params={},
+        project=project)
+
+    with pytest.raises(NotSupportedException):
+        svc.train(document_corpus)
+
+
 def test_svc_train_nodocuments(datadir, project, empty_corpus):
     svc_type = annif.backend.get_backend('svc')
     svc = svc_type(