diff --git a/spec/ruby/optional/capi/fixnum_spec.rb b/spec/ruby/optional/capi/fixnum_spec.rb
index d6bb06b1f1..dffe3da0bb 100644
--- a/spec/ruby/optional/capi/fixnum_spec.rb
+++ b/spec/ruby/optional/capi/fixnum_spec.rb
@@ -25,7 +25,7 @@ describe "CApiFixnumSpecs" do
       end
     end
 
-    platform_is_not :windows do
+    platform_is wordsize: 64 do # sizeof(long) > sizeof(int)
       it "raises a TypeError if passed nil" do
         lambda { @s.FIX2INT(nil) }.should raise_error(TypeError)
       end
@@ -74,7 +74,7 @@ describe "CApiFixnumSpecs" do
       end
     end
 
-    platform_is_not :windows do
+    platform_is wordsize: 64 do # sizeof(long) > sizeof(int)
       it "raises a TypeError if passed nil" do
         lambda { @s.FIX2UINT(nil) }.should raise_error(TypeError)
       end