diff --git a/src/main/java/nl/knaw/dans/dvcli/action/SingleIdOrIdsFile.java b/src/main/java/nl/knaw/dans/dvcli/action/SingleIdOrIdsFile.java
index 97f6ac6..6b1b9d7 100644
--- a/src/main/java/nl/knaw/dans/dvcli/action/SingleIdOrIdsFile.java
+++ b/src/main/java/nl/knaw/dans/dvcli/action/SingleIdOrIdsFile.java
@@ -38,7 +38,7 @@ public Stream<String> getPids() throws IOException {
             return Stream.of(defaultId);
         }
 
-        Stream<String> lines = null;
+        Stream<String> lines;
 
         if ("-".equals(singleIdOrIdFile)) {
             BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
@@ -47,6 +47,9 @@ public Stream<String> getPids() throws IOException {
         else {
             var pidFile = Paths.get(singleIdOrIdFile);
             if (Files.exists(pidFile)) {
+                if (!Files.isRegularFile(pidFile)) {
+                    throw new IOException(singleIdOrIdFile + " is not a regular file");
+                }
                 lines = Files.lines(pidFile)
                     .flatMap(line -> Arrays.stream(line.trim().split("\\s+")));
             }
diff --git a/src/test/java/nl/knaw/dans/dvcli/action/SingleOrTest.java b/src/test/java/nl/knaw/dans/dvcli/action/SingleOrTest.java
index e22cc42..1025698 100644
--- a/src/test/java/nl/knaw/dans/dvcli/action/SingleOrTest.java
+++ b/src/test/java/nl/knaw/dans/dvcli/action/SingleOrTest.java
@@ -25,8 +25,8 @@
 import org.mockito.Mockito;
 
 import java.io.ByteArrayInputStream;
+import java.io.IOException;
 import java.io.InputStream;
-import java.io.UncheckedIOException;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.nio.file.Files;
@@ -36,7 +36,6 @@
 import static nl.knaw.dans.dvcli.action.SingleIdOrIdsFile.DEFAULT_TARGET_PLACEHOLDER;
 import static org.assertj.core.api.AssertionsForClassTypes.assertThatThrownBy;
 import static org.assertj.core.api.AssertionsForInterfaceTypes.assertThat;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
@@ -112,11 +111,10 @@ public void getDatasets_should_parse_file_with_white_space() throws Exception {
     @Test
     public void getDatasets_should_throw_when_parsing_a_directory() throws Exception {
 
-        var datasets = new SingleDatasetOrDatasetsFile("target", getClient())
-            .getDatasets();
-        var exception = assertThrows(RuntimeException.class, datasets::toList);
-        assertThat( exception.getMessage())
-            .isEqualTo("java.io.IOException: Is a directory");
+        var ids = new SingleDatasetOrDatasetsFile("target", getClient());
+        assertThatThrownBy(ids::getDatasets)
+            .isInstanceOf(IOException.class)
+            .hasMessage("target is not a regular file");
     }
 
     @Test