diff --git a/JSIL/ILBlockTranslator.cs b/JSIL/ILBlockTranslator.cs
index a93fc3b4b..2da7af1b9 100644
--- a/JSIL/ILBlockTranslator.cs
+++ b/JSIL/ILBlockTranslator.cs
@@ -547,6 +547,23 @@ protected JSExpression Translate_BinaryOp (ILExpression node, JSBinaryOperator o
                 AutoCastingState.Pop();
             }
 
+            if (node.Code.GetName().Contains(".un"))
+            {
+                var lType = lhs.GetActualType(TypeSystem);
+                var lUnsigned = TypeUtil.GetUnsignedType(lType, TypeSystem);
+                if (lType != lUnsigned)
+                {
+                    lhs = JSCastExpression.New(lhs, lUnsigned, TypeSystem, isCoercion: true);
+                }
+
+                var rType = rhs.GetActualType(TypeSystem);
+                var rUnsigned = TypeUtil.GetUnsignedType(rType, TypeSystem);
+                if (lType != rUnsigned)
+                {
+                    rhs = JSCastExpression.New(rhs, rUnsigned, TypeSystem, isCoercion: true);
+                }
+            }
+
             if (TypeUtil.IsPointer(lhs.GetActualType(TypeSystem)))
                 arePointersInvolved |= true;
             else if (TypeUtil.IsPointer(rhs.GetActualType(TypeSystem)))
diff --git a/JSIL/TypeUtil.cs b/JSIL/TypeUtil.cs
index 65d43a67e..eea595b10 100644
--- a/JSIL/TypeUtil.cs
+++ b/JSIL/TypeUtil.cs
@@ -163,6 +163,40 @@ public static bool IsNumeric (TypeReference type) {
             }
         }
 
+        public static TypeReference GetUnsignedType(TypeReference type, TypeSystem typeSystem)
+        {
+            type = DereferenceType(type);
+
+            switch (type.MetadataType)
+            {
+                case MetadataType.UIntPtr:
+                case MetadataType.IntPtr:
+                    return typeSystem.UIntPtr;
+
+                case MetadataType.SByte:
+                case MetadataType.Byte:
+                    return typeSystem.Byte;
+
+                case MetadataType.Int16:
+                case MetadataType.UInt16:
+                    return typeSystem.UInt16;
+
+                case MetadataType.Int32:
+                case MetadataType.UInt32:
+                    return typeSystem.UInt32;
+
+                case MetadataType.Int64:
+                case MetadataType.UInt64:
+                    return typeSystem.UInt64;
+
+                case MetadataType.Char:
+                    return typeSystem.Char;
+
+                default:
+                    return type;
+            }
+        }
+
         public static bool? IsSigned (TypeReference type) {
             type = DereferenceType(type);
 
diff --git a/Tests/SimpleTestCases/ble.un.il b/Tests/SimpleTestCases/ble.un.il
new file mode 100644
index 000000000..27cdccc4e
--- /dev/null
+++ b/Tests/SimpleTestCases/ble.un.il
@@ -0,0 +1,27 @@
+.assembly Hello {}
+.assembly extern mscorlib {}
+
+.class public abstract sealed Program
+	extends [mscorlib]System.Object
+{
+	.method static void Main()
+	{
+		.entrypoint
+		.maxstack 1
+
+		ldc.i4       -1
+		ldc.i4.5 
+		ble.un.s     END
+		ldstr        "int32"
+		call         void [mscorlib]System.Console::WriteLine(string)
+
+		ldc.i8       -1
+		ldc.i8       5 
+		ble.un.s     END
+		ldstr        "int64"
+		call         void [mscorlib]System.Console::WriteLine(string)
+
+		END:
+		ret
+	}
+}
\ No newline at end of file
diff --git a/Tests/SimpleTests.csproj b/Tests/SimpleTests.csproj
index fe2112c10..c56b4840a 100644
--- a/Tests/SimpleTests.csproj
+++ b/Tests/SimpleTests.csproj
@@ -66,6 +66,7 @@
   <ItemGroup>
     <None Include="app.config" />
     <None Include="packages.config" />
+    <None Include="SimpleTestCases\ble.un.il" />
     <None Include="SimpleTestCases\Issue538.cs" />
     <None Include="SimpleTestCases\Issue567.cs" />
     <None Include="SimpleTestCasesForStubbedBcl\Issue585.cs" />