diff --git a/include/prism/internal/bit.h b/include/prism/internal/bit.h
index b0111a4c2c..4f7b56090f 100644
--- a/include/prism/internal/bit.h
+++ b/include/prism/internal/bit.h
@@ -12,7 +12,7 @@
  */
 #if defined(__GNUC__) || defined(__clang__)
 #define pm_ctzll(v) ((unsigned) __builtin_ctzll(v))
-#elif defined(_MSC_VER)
+#elif defined(_MSC_VER) && defined(_WIN64)
 #include <intrin.h>
 #include <stdint.h>
 
diff --git a/lib/prism/ffi.rb b/lib/prism/ffi.rb
index 192b7cb52e..6eb8231c2c 100644
--- a/lib/prism/ffi.rb
+++ b/lib/prism/ffi.rb
@@ -186,7 +186,7 @@ def self.with
     # pointer directly; for files it uses a pm_source_t under the hood.
     class PrismSource # :nodoc:
       PLATFORM_EXPECTS_UTF8 =
-        RbConfig::CONFIG["host_os"].match?(/bccwin|cygwin|djgpp|mingw|mswin|wince|darwin/i)
+        RbConfig::CONFIG["host_os"].match?(/cygwin|mingw|mswin|darwin/i)
 
       attr_reader :pointer, :length
 
diff --git a/test/prism/test_helper.rb b/test/prism/test_helper.rb
index 406582c0a5..9fea36476b 100644
--- a/test/prism/test_helper.rb
+++ b/test/prism/test_helper.rb
@@ -236,7 +236,7 @@ def self.each_encoding
 
     # True if the current platform is Windows.
     def self.windows?
-      RbConfig::CONFIG["host_os"].match?(/bccwin|cygwin|djgpp|mingw|mswin|wince/i)
+      RbConfig::CONFIG["host_os"].match?(/cygwin|mingw|mswin/i)
     end
 
     # All versions that prism can parse