diff --git a/src/wren_core.c b/src/wren_core.c
index d9df032b..6909de96 100644
--- a/src/wren_core.c
+++ b/src/wren_core.c
@@ -878,12 +878,6 @@ DEF_PRIMITIVE(num_cos)
   RETURN_NUM(cos(AS_NUM(args[0])));
 }
 
-DEF_PRIMITIVE(num_decimal)
-{
-  double value = AS_NUM(args[0]);
-  RETURN_NUM(value - (int32_t)value);
-}
-
 DEF_PRIMITIVE(num_deg)
 {
   RETURN_NUM(floor(AS_NUM(args[0]) * 57.2957795130823208768));
@@ -901,6 +895,13 @@ DEF_PRIMITIVE(num_floor)
   RETURN_NUM(floor(AS_NUM(args[0])));
 }
 
+DEF_PRIMITIVE(num_fraction)
+{
+  double integer;
+  double fractional = modf(AS_NUM(args[0]) , &integer);
+  RETURN_NUM(fractional);
+}
+
 DEF_PRIMITIVE(num_isNan)
 {
   RETURN_BOOL(isnan(AS_NUM(args[0])));
@@ -1557,10 +1558,10 @@ void wrenInitializeCore(WrenVM* vm)
   PRIMITIVE(vm->numClass, "abs", num_abs);
   PRIMITIVE(vm->numClass, "ceil", num_ceil);
   PRIMITIVE(vm->numClass, "cos", num_cos);
-  PRIMITIVE(vm->numClass, "decimal", num_decimal);
   PRIMITIVE(vm->numClass, "deg", num_deg);
   PRIMITIVE(vm->numClass, "div(_)", num_div);
   PRIMITIVE(vm->numClass, "floor", num_floor);
+  PRIMITIVE(vm->numClass, "fraction", num_fraction);
   PRIMITIVE(vm->numClass, "isNan", num_isNan);
   PRIMITIVE(vm->numClass, "rad", num_rad);
   PRIMITIVE(vm->numClass, "sign", num_sign);