diff --git a/src/MongoDB.Bson/IO/JsonReader.cs b/src/MongoDB.Bson/IO/JsonReader.cs
index 54b98d08eba..f6480420eb9 100644
--- a/src/MongoDB.Bson/IO/JsonReader.cs
+++ b/src/MongoDB.Bson/IO/JsonReader.cs
@@ -1961,13 +1961,13 @@ private BsonValue ParseTimestampConstructor()
             VerifyToken(",");
             int increment;
             var incrementToken = PopToken();
-            if (secondsSinceEpochToken.IsNumber)
+            if (incrementToken.IsNumber)
             {
                 increment = incrementToken.Int32Value;
             }
             else
             {
-                var message = string.Format("JSON reader expected a number but found '{0}'.", secondsSinceEpochToken.Lexeme);
+                var message = string.Format("JSON reader expected a number but found '{0}'.", incrementToken.Lexeme);
                 throw new FormatException(message);
             }
             VerifyToken(")");
diff --git a/tests/MongoDB.Bson.Tests/IO/JsonReaderTests.cs b/tests/MongoDB.Bson.Tests/IO/JsonReaderTests.cs
index 76c31fa01cd..4cf30d92361 100644
--- a/tests/MongoDB.Bson.Tests/IO/JsonReaderTests.cs
+++ b/tests/MongoDB.Bson.Tests/IO/JsonReaderTests.cs
@@ -1396,6 +1396,26 @@ public void TestTimestampConstructor()
             Assert.Equal(json, BsonSerializer.Deserialize<BsonTimestamp>(new StringReader(json)).ToJson());
         }
 
+        [Theory]
+        // truncated input
+        [InlineData("Timestamp(")]
+        [InlineData("Timestamp()")]
+        [InlineData("Timestamp(1")]
+        [InlineData("Timestamp(1,")]
+        [InlineData("Timestamp(1, 2")]
+        // valid JSON but not a valid extended JSON BsonTimestamp
+        [InlineData("Timestamp('abc', 2)")]
+        [InlineData("Timestamp(2, 'abc')")]
+        public void TestTimestampConstructorWhenInvalid(string json)
+        {
+            using (_bsonReader = new JsonReader(json))
+            {
+                var exception = Record.Exception(() => _bsonReader.ReadBsonType());
+
+                exception.Should().BeOfType<FormatException>();
+            }
+        }
+
         [Theory]
         [InlineData("{ \"$timestamp\" : { \"t\" : 1, \"i\" : 2 } }")]
         [InlineData("{ \"$timestamp\" : { \"i\" : 2, \"t\" : 1 } }")]