diff --git a/compiler/compile-unit.go b/compiler/compile-unit.go
index b1377f7..7433a8b 100644
--- a/compiler/compile-unit.go
+++ b/compiler/compile-unit.go
@@ -35,7 +35,9 @@ func (this *Compiler) CompileUnit (address entity.Address) error {
 	// extension of the input. if that isn't specified, default to .o
 	if this.Filetype == FiletypeUnknown {
 		var ok bool
-		this.Filetype, ok = FiletypeFromExt(filepath.Ext(this.Output))
+		this.Filetype, ok = FiletypeFromExt (
+			*this.Target,
+			filepath.Ext(this.Output))
 		if !ok {
 			this.Filetype = FiletypeObject
 		}
@@ -46,7 +48,7 @@ func (this *Compiler) CompileUnit (address entity.Address) error {
 	if this.Output == "" {
 		nickname, ok := entity.Address(path).Nickname()
 		if !ok { nickname = "output" }
-		this.Output = this.Filetype.Extend(nickname)
+		this.Output = this.Filetype.Extend(*this.Target, nickname)
 	}
 
 	// do something based on the output extension
diff --git a/compiler/filetype.go b/compiler/filetype.go
index e229b10..040ea7b 100644
--- a/compiler/filetype.go
+++ b/compiler/filetype.go
@@ -1,6 +1,7 @@
 package compiler
 
 import "fmt"
+import "git.tebibyte.media/fspl/fspl/generator"
 
 // Filetype represents an output filetype.
 type Filetype int; const (
@@ -24,15 +25,13 @@ func FiletypeFromString (ext string) (Filetype, bool) {
 }
 
 // FiletypeFromExt returns a filetype based on the given filename extension.
-func FiletypeFromExt (ext string) (Filetype, bool) {
-	// FIXME some of these are platform dependent, for example on windows
-	// FiletypeLib would be .dll
+func FiletypeFromExt (target generator.Target, ext string) (Filetype, bool) {
 	switch ext {
-	case ".o":  return FiletypeObject,   true
-	case ".so": return FiletypeLibrary,  true
-	case ".s":  return FiletypeAssembly, true
-	case ".ll": return FiletypeIR,       true
-	default:    return FiletypeUnknown,  false
+	case ".o":                return FiletypeObject,   true
+	case targetSoExt(target): return FiletypeLibrary,  true
+	case ".s":                return FiletypeAssembly, true
+	case ".ll":               return FiletypeIR,       true
+	default:                  return FiletypeUnknown,  false
 	}
 }
 
@@ -49,12 +48,11 @@ func (filetype Filetype) String () string {
 }
 
 // Ext returns the standard filename extension of the filetype.
-func (filetype Filetype) Ext () string {
-	// FIXME again, some of these are platform dependent
+func (filetype Filetype) Ext (target generator.Target) string {
 	switch filetype {
 	case FiletypeUnknown:  return ""
 	case FiletypeObject:   return ".o"
-	case FiletypeLibrary:  return ".so"
+	case FiletypeLibrary:  return targetSoExt(target)
 	case FiletypeAssembly: return ".s"
 	case FiletypeIR:       return ".ll"
 	default:               return ""
@@ -62,6 +60,14 @@ func (filetype Filetype) Ext () string {
 }
 
 // Extend adds the extension of the filetype onto the specified path.
-func (filetype Filetype) Extend (path string) string {
-	return path + filetype.Ext()
+func (filetype Filetype) Extend (target generator.Target, path string) string {
+	return path + filetype.Ext(target)
+}
+
+func targetSoExt (target generator.Target) string {
+	// TODO: more research is required here
+	switch target.OS {
+	case "windows": return ".dll"
+	default:        return ".so"
+	}
 }