diff --git a/sv-parser-pp/src/preprocess.rs b/sv-parser-pp/src/preprocess.rs
index e0a6c99..92f4b5c 100644
--- a/sv-parser-pp/src/preprocess.rs
+++ b/sv-parser-pp/src/preprocess.rs
@@ -1550,4 +1550,21 @@ mod tests {
             testfile_contents("timescale.sv")
         );
     } // }}}
+
+    #[test]
+    fn unconnected_drive() { // {{{
+        let include_paths = [testfile_path("")];
+        let (ret, _) = preprocess(
+            testfile_path("unconnected_drive.sv"),
+            &HashMap::new(),
+            &include_paths,
+            false,
+            false,
+        )
+        .unwrap();
+        assert_eq!(
+            ret.text(),
+            testfile_contents("unconnected_drive.sv")
+        );
+    } // }}}
 }
diff --git a/sv-parser-pp/testcases/unconnected_drive.sv b/sv-parser-pp/testcases/unconnected_drive.sv
new file mode 100644
index 0000000..e48f549
--- /dev/null
+++ b/sv-parser-pp/testcases/unconnected_drive.sv
@@ -0,0 +1,13 @@
+// IEEE1800-2017 Clause 22.9
+// The directive `unconnected_drive takes one of two arguments - pull1 or
+// pull 0. When pull1 is specified, unconnected ports are pulled down. It is
+// advisable to pair each `unconnected_drive with a
+// `nounconnected_drive, but it is not required. The latest occurrence of
+// either directive in the source controls what happens to unconnected ports.
+// These directives shall be specified outside the design element declarations.
+// The `resetall directive includes the effects of a `nounconnected
+// directive.
+`unconnected_drive pull0
+`unconnected_drive pull1
+`nounconnected_drive
+// This file should be emitted from the preprocessor unchanged.