diff --git a/ChangeLog b/ChangeLog
index 7cde69e..41408e6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Tue May 26 12:21:18 2009  Minero Aoki  <aamine@loveruby.net>
+
+	* net/loveruby/cflat/compiler/Options.java: check unknown file
+	  types.
+
+	* net/loveruby/cflat/compiler/SourceFile.java: new method
+	  #isKnownFileType.
+
 Tue May 26 11:59:08 2009  Minero Aoki  <aamine@loveruby.net>
 
 	* net/loveruby/cflat/compiler/Options.java: allow --verbose-asm
diff --git a/net/loveruby/cflat/compiler/Compiler.java b/net/loveruby/cflat/compiler/Compiler.java
index 81c4d9d..f1149ab 100644
--- a/net/loveruby/cflat/compiler/Compiler.java
+++ b/net/loveruby/cflat/compiler/Compiler.java
@@ -49,7 +49,7 @@ public class Compiler {
         }
         catch (OptionParseError err) {
             errorHandler.error(err.getMessage());
-            errorHandler.error("Try cbc --help for option usage");
+            errorHandler.error("Try \"cbc --help\" for usage");
             System.exit(1);
             return null;   // never reach
         }
diff --git a/net/loveruby/cflat/compiler/Options.java b/net/loveruby/cflat/compiler/Options.java
index 120638a..58cd3a9 100644
--- a/net/loveruby/cflat/compiler/Options.java
+++ b/net/loveruby/cflat/compiler/Options.java
@@ -176,8 +176,8 @@ class Options {
                     }
                     genOptions.setOptimizationLevel(type.equals("0") ? 0 : 1);
                 }
-                else if (arg.equals("--verbose-asm")
-                        || arg.equals("-fverbose-asm")) {
+                else if (arg.equals("-fverbose-asm")
+                        || arg.equals("--verbose-asm")) {
                     genOptions.generateVerboseAsm();
                 }
                 else if (arg.startsWith("-Wa,")) {
@@ -263,6 +263,11 @@ class Options {
         if (sourceFiles.isEmpty()) {
             parseError("no input file");
         }
+        for (SourceFile src : sourceFiles) {
+            if (! src.isKnownFileType()) {
+                parseError("unknown file type: " + src.path());
+            }
+        }
         if (outputFileName != null
                 && sourceFiles.size() > 1
                 && ! isLinkRequired()) {
@@ -334,6 +339,12 @@ class Options {
         out.println("  --version        Shows compiler version and quit.");
         out.println("  --help           Prints this message and quit.");
         out.println("");
+        out.println("Optimization Options:");
+        out.println("  -O               Enables optimization.");
+        out.println("  -O1, -O2, -O3    Equivalent to -O.");
+        out.println("  -Os              Equivalent to -O.");
+        out.println("  -O0              Disables optimization (default).");
+        out.println("");
         out.println("Parser Options:");
         out.println("  -I PATH          Adds PATH as import file directory.");
         out.println("  --debug-parser   Dumps parsing process.");
@@ -347,7 +358,7 @@ class Options {
         out.println("  -fpic            Equivalent to -fPIC.");
         out.println("  -fPIE            Generates PIE assembly.");
         out.println("  -fpie            Equivalent to -fPIE.");
-        out.println("  --verbose-asm    Generate assembly with verbose comments.");
+        out.println("  -fverbose-asm    Generate assembly with verbose comments.");
         out.println("");
         out.println("Assembler Options:");
         out.println("  -Wa,OPT          Passes OPT to the assembler (as).");
diff --git a/net/loveruby/cflat/compiler/SourceFile.java b/net/loveruby/cflat/compiler/SourceFile.java
index f2bf835..c49fbb4 100644
--- a/net/loveruby/cflat/compiler/SourceFile.java
+++ b/net/loveruby/cflat/compiler/SourceFile.java
@@ -2,7 +2,23 @@ package net.loveruby.cflat.compiler;
 import java.io.File;
 
 class SourceFile implements LdArg {
-    private String originalName;
+    static final String EXT_CFLAT_SOURCE = ".cb";
+    static final String EXT_ASSEMBLY_SOURCE = ".s";
+    static final String EXT_OBJECT_FILE = ".o";
+    static final String EXT_STATIC_LIBRARY = ".a";
+    static final String EXT_SHARED_LIBRARY = ".so";
+    static final String EXT_EXECUTABLE_FILE = "";
+
+    static final String[] KNOWN_EXTENSIONS = {
+      EXT_CFLAT_SOURCE,
+      EXT_ASSEMBLY_SOURCE,
+      EXT_OBJECT_FILE,
+      EXT_STATIC_LIBRARY,
+      EXT_SHARED_LIBRARY,
+      EXT_EXECUTABLE_FILE
+    };
+
+    private final String originalName;
     private String currentName;
 
     SourceFile(String name) {
@@ -30,36 +46,44 @@ class SourceFile implements LdArg {
         this.currentName = name;
     }
 
+    boolean isKnownFileType() {
+        String ext = extName(originalName);
+        for (String e : KNOWN_EXTENSIONS) {
+            if (e.equals(ext)) return true;
+        }
+        return false;
+    }
+
     boolean isCflatSource() {
-        return extName(currentName).equals(".cb");
+        return extName(currentName).equals(EXT_CFLAT_SOURCE);
     }
 
     boolean isAssemblySource() {
-        return extName(currentName).equals(".s");
+        return extName(currentName).equals(EXT_ASSEMBLY_SOURCE);
     }
 
     boolean isObjectFile() {
-        return extName(currentName).equals(".o");
+        return extName(currentName).equals(EXT_OBJECT_FILE);
     }
 
     boolean isSharedLibrary() {
-        return extName(currentName).equals(".so");
+        return extName(currentName).equals(EXT_SHARED_LIBRARY);
     }
 
     boolean isStaticLibrary() {
-        return extName(currentName).equals(".a");
+        return extName(currentName).equals(EXT_STATIC_LIBRARY);
     }
 
     boolean isExecutable() {
-        return extName(currentName).equals("");
+        return extName(currentName).equals(EXT_EXECUTABLE_FILE);
     }
 
     String asmFileName() {
-        return replaceExt(".s");
+        return replaceExt(EXT_ASSEMBLY_SOURCE);
     }
 
     String objFileName() {
-        return replaceExt(".o");
+        return replaceExt(EXT_OBJECT_FILE);
     }
 
     String linkedFileName(String newExt) {