diff --git a/src/main/java/io/reactivex/internal/functions/Functions.java b/src/main/java/io/reactivex/internal/functions/Functions.java
index 5d562a8b76..b54694844f 100644
--- a/src/main/java/io/reactivex/internal/functions/Functions.java
+++ b/src/main/java/io/reactivex/internal/functions/Functions.java
@@ -24,7 +24,7 @@
 import io.reactivex.schedulers.Timed;
 
 /**
- * Utility methods to convert the Function3..Function9 instances to Function of Object array.
+ * Utility methods to convert the BiFunction, Function3..Function9 instances to Function of Object array.
  */
 public final class Functions {
 
diff --git a/src/test/java/io/reactivex/internal/functions/FunctionsTest.java b/src/test/java/io/reactivex/internal/functions/FunctionsTest.java
index bea758be58..872d09df15 100644
--- a/src/test/java/io/reactivex/internal/functions/FunctionsTest.java
+++ b/src/test/java/io/reactivex/internal/functions/FunctionsTest.java
@@ -169,6 +169,62 @@ public Integer apply(Integer t1, Integer t2, Integer t3, Integer t4, Integer t5,
         }).apply(new Object[20]);
     }
 
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Test(expected = NullPointerException.class)
+    public void biFunctionFail() throws Exception {
+        BiFunction biFunction = null;
+        Functions.toFunction(biFunction);
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Test(expected = NullPointerException.class)
+    public void function3Fail() throws Exception {
+        Function3 function3 = null;
+        Functions.toFunction(function3);
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Test(expected = NullPointerException.class)
+    public void function4Fail() throws Exception {
+        Function4 function4 = null;
+        Functions.toFunction(function4);
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Test(expected = NullPointerException.class)
+    public void function5Fail() throws Exception {
+        Function5 function5 = null;
+        Functions.toFunction(function5);
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Test(expected = NullPointerException.class)
+    public void function6Fail() throws Exception {
+        Function6 function6 = null;
+        Functions.toFunction(function6);
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Test(expected = NullPointerException.class)
+    public void function7Fail() throws Exception {
+        Function7 function7 = null;
+        Functions.toFunction(function7);
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Test(expected = NullPointerException.class)
+    public void function8Fail() throws Exception {
+        Function8 function8 = null;
+        Functions.toFunction(function8);
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    @Test(expected = NullPointerException.class)
+    public void function9Fail() throws Exception {
+        Function9 function9 = null;
+        Functions.toFunction(function9);
+    }
+
     @Test
     public void identityFunctionToString() {
         assertEquals("IdentityFunction", Functions.identity().toString());