diff --git a/src/main/java/com/greplin/interval/LongInterval.java b/src/main/java/com/greplin/interval/LongInterval.java
index 63dc3bd..890ceb6 100644
--- a/src/main/java/com/greplin/interval/LongInterval.java
+++ b/src/main/java/com/greplin/interval/LongInterval.java
@@ -105,9 +105,13 @@ public boolean intersects(final LongInterval other) {
   public static LongInterval valueOf(final String value) {
     String trimmed = value.trim();
     int middle = trimmed.indexOf('-', 1);
-    long start = Long.parseLong(trimmed.substring(0, middle).trim());
-    long end = Long.parseLong(trimmed.substring(middle + 1).trim());
-    return new LongInterval(start, end);
+    try {
+        long start = Long.parseLong(trimmed.substring(0, middle).trim());
+        long end = Long.parseLong(trimmed.substring(middle + 1).trim());
+        return new LongInterval(start, end);
+    } catch(NumberFormatException e) {
+        throw new NumberFormatException("Passed value does not contain two parsable long values");
+    }
   }
 
 
diff --git a/src/test/java/com/greplin/interval/LongIntervalTest.java b/src/test/java/com/greplin/interval/LongIntervalTest.java
index 5475043..9a629e8 100644
--- a/src/test/java/com/greplin/interval/LongIntervalTest.java
+++ b/src/test/java/com/greplin/interval/LongIntervalTest.java
@@ -21,6 +21,11 @@ public void testNegativeNumbers() throws Exception {
     assertParse("-2--1", -2, -1);
   }
 
+  @Test(expected=NumberFormatException.class)
+  public void testEmptyNumbers() throws Exception {
+    LongInterval result = LongInterval.valueOf("null-null");
+  }
+
   @Test
   public void testEquals() throws Exception {
     Assert.assertEquals(new LongInterval(1, 100), new LongInterval(1, 100));