diff --git a/main.c b/main.c
index 27bcadf..398108b 100644
--- a/main.c
+++ b/main.c
@@ -1,8 +1,11 @@
 #include "chibicc.h"
 
+typedef enum { FILE_NONE, FILE_C, FILE_ASM, FILE_OBJ } FileType;
+
 StringArray include_paths;
 bool opt_fcommon = true;
 
+static FileType opt_x;
 static StringArray opt_include;
 static bool opt_E;
 static bool opt_S;
@@ -23,7 +26,7 @@ static void usage(int status) {
 }
 
 static bool take_arg(char *arg) {
-  char *x[] = {"-o", "-I", "-idirafter", "-include"};
+  char *x[] = {"-o", "-I", "-idirafter", "-include", "-x"};
 
   for (int i = 0; i < sizeof(x) / sizeof(*x); i++)
     if (!strcmp(arg, x[i]))
@@ -50,6 +53,16 @@ static void define(char *str) {
     define_macro(str, "1");
 }
 
+static FileType parse_opt_x(char *s) {
+  if (!strcmp(s, "c"))
+    return FILE_C;
+  if (!strcmp(s, "assembler"))
+    return FILE_ASM;
+  if (!strcmp(s, "none"))
+    return FILE_NONE;
+  error("<command line>: unknown argument for -x: %s", s);
+}
+
 static void parse_args(int argc, char **argv) {
   // Make sure that all command line options that take an argument
   // have an argument.
@@ -139,6 +152,16 @@ static void parse_args(int argc, char **argv) {
       continue;
     }
 
+    if (!strcmp(argv[i], "-x")) {
+      opt_x = parse_opt_x(argv[++i]);
+      continue;
+    }
+
+    if (!strncmp(argv[i], "-x", 2)) {
+      opt_x = parse_opt_x(argv[i] + 2);
+      continue;
+    }
+
     if (!strcmp(argv[i], "-cc1-input")) {
       base_file = argv[++i];
       continue;
@@ -434,6 +457,21 @@ static void run_linker(StringArray *inputs, char *output) {
   run_subprocess(arr.data);
 }
 
+static FileType get_file_type(char *filename) {
+  if (endswith(filename, ".o"))
+    return FILE_OBJ;
+
+  if (opt_x != FILE_NONE)
+    return opt_x;
+
+  if (endswith(filename, ".c"))
+    return FILE_C;
+  if (endswith(filename, ".s"))
+    return FILE_ASM;
+
+  error("<command line>: unknown file extension: %s", filename);
+}
+
 int main(int argc, char **argv) {
   atexit(cleanup);
   init_macros();
@@ -461,22 +499,22 @@ int main(int argc, char **argv) {
     else
       output = replace_extn(input, ".o");
 
+    FileType type = get_file_type(input);
+
     // Handle .o
-    if (endswith(input, ".o")) {
+    if (type == FILE_OBJ) {
       strarray_push(&ld_args, input);
       continue;
     }
 
     // Handle .s
-    if (endswith(input, ".s")) {
+    if (type == FILE_ASM) {
       if (!opt_S)
         assemble(input, output);
       continue;
     }
 
-    // Handle .c
-    if (!endswith(input, ".c") && strcmp(input, "-"))
-      error("unknown file extension: %s", input);
+    assert(type == FILE_C);
 
     // Just preprocess
     if (opt_E) {
diff --git a/test/driver.sh b/test/driver.sh
index 2fdf08a..3f31b4f 100755
--- a/test/driver.sh
+++ b/test/driver.sh
@@ -25,7 +25,7 @@ $chibicc --help 2>&1 | grep -q chibicc
 check --help
 
 # -S
-echo 'int main() {}' | $chibicc -S -o - - | grep -q 'main:'
+echo 'int main() {}' | $chibicc -S -o- -xc - | grep -q 'main:'
 check -S
 
 # Default output file
@@ -56,7 +56,7 @@ check 'multiple input files'
 
 # Run linker
 rm -f $tmp/foo
-echo 'int main() { return 0; }' | $chibicc -o $tmp/foo -
+echo 'int main() { return 0; }' | $chibicc -o $tmp/foo -xc -xc -
 $tmp/foo
 check linker
 
@@ -77,30 +77,30 @@ check a.out
 
 # -E
 echo foo > $tmp/out
-echo "#include \"$tmp/out\"" | $chibicc -E - | grep -q foo
+echo "#include \"$tmp/out\"" | $chibicc -E -xc - | grep -q foo
 check -E
 
 echo foo > $tmp/out1
-echo "#include \"$tmp/out1\"" | $chibicc -E -o $tmp/out2 -
+echo "#include \"$tmp/out1\"" | $chibicc -E -o $tmp/out2 -xc -
 cat $tmp/out2 | grep -q foo
 check '-E and -o'
 
 # -I
 mkdir $tmp/dir
 echo foo > $tmp/dir/i-option-test
-echo "#include \"i-option-test\"" | $chibicc -I$tmp/dir -E - | grep -q foo
+echo "#include \"i-option-test\"" | $chibicc -I$tmp/dir -E -xc - | grep -q foo
 check -I
 
 # -D
-echo foo | $chibicc -Dfoo -E - | grep -q 1
+echo foo | $chibicc -Dfoo -E -xc - | grep -q 1
 check -D
 
 # -D
-echo foo | $chibicc -Dfoo=bar -E - | grep -q bar
+echo foo | $chibicc -Dfoo=bar -E -xc - | grep -q bar
 check -D
 
 # -U
-echo foo | $chibicc -Dfoo=bar -Ufoo -E - | grep -q foo
+echo foo | $chibicc -Dfoo=bar -Ufoo -E -xc - | grep -q foo
 check -U
 
 # ignored options
@@ -110,7 +110,7 @@ $chibicc -c -O -Wall -g -std=c11 -ffreestanding -fno-builtin \
 check 'ignored options'
 
 # BOM marker
-printf '\xef\xbb\xbfxyz\n' | $chibicc -E -o- - | grep -q '^xyz'
+printf '\xef\xbb\xbfxyz\n' | $chibicc -E -o- -xc - | grep -q '^xyz'
 check 'BOM marker'
 
 # Inline functions
@@ -125,67 +125,77 @@ echo 'int foo(); int main() { foo(); }' > $tmp/inline2.c
 $chibicc -o /dev/null $tmp/inline1.c $tmp/inline2.c
 check inline
 
-echo 'static inline void f1() {}' | $chibicc -o- -S - | grep -v -q f1:
+echo 'static inline void f1() {}' | $chibicc -o- -S -xc - | grep -v -q f1:
 check inline
 
-echo 'static inline void f1() {} void foo() { f1(); }' | $chibicc -o- -S - | grep -q f1:
+echo 'static inline void f1() {} void foo() { f1(); }' | $chibicc -o- -S -xc - | grep -q f1:
 check inline
 
-echo 'static inline void f1() {} static inline void f2() { f1(); } void foo() { f1(); }' | $chibicc -o- -S - | grep -q f1:
+echo 'static inline void f1() {} static inline void f2() { f1(); } void foo() { f1(); }' | $chibicc -o- -S -xc - | grep -q f1:
 check inline
 
-echo 'static inline void f1() {} static inline void f2() { f1(); } void foo() { f1(); }' | $chibicc -o- -S - | grep -v -q f2:
+echo 'static inline void f1() {} static inline void f2() { f1(); } void foo() { f1(); }' | $chibicc -o- -S -xc - | grep -v -q f2:
 check inline
 
-echo 'static inline void f1() {} static inline void f2() { f1(); } void foo() { f2(); }' | $chibicc -o- -S - | grep -q f1:
+echo 'static inline void f1() {} static inline void f2() { f1(); } void foo() { f2(); }' | $chibicc -o- -S -xc - | grep -q f1:
 check inline
 
-echo 'static inline void f1() {} static inline void f2() { f1(); } void foo() { f2(); }' | $chibicc -o- -S - | grep -q f2:
+echo 'static inline void f1() {} static inline void f2() { f1(); } void foo() { f2(); }' | $chibicc -o- -S -xc - | grep -q f2:
 check inline
 
-echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() {}' | $chibicc -o- -S - | grep -v -q f1:
+echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() {}' | $chibicc -o- -S -xc - | grep -v -q f1:
 check inline
 
-echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() {}' | $chibicc -o- -S - | grep -v -q f2:
+echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() {}' | $chibicc -o- -S -xc - | grep -v -q f2:
 check inline
 
-echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() { f1(); }' | $chibicc -o- -S - | grep -q f1:
+echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() { f1(); }' | $chibicc -o- -S -xc - | grep -q f1:
 check inline
 
-echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() { f1(); }' | $chibicc -o- -S - | grep -q f2:
+echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() { f1(); }' | $chibicc -o- -S -xc - | grep -q f2:
 check inline
 
-echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() { f2(); }' | $chibicc -o- -S - | grep -q f1:
+echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() { f2(); }' | $chibicc -o- -S -xc - | grep -q f1:
 check inline
 
-echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() { f2(); }' | $chibicc -o- -S - | grep -q f2:
+echo 'static inline void f2(); static inline void f1() { f2(); } static inline void f2() { f1(); } void foo() { f2(); }' | $chibicc -o- -S -xc - | grep -q f2:
 check inline
 
 # -idirafter
 mkdir -p $tmp/dir1 $tmp/dir2
 echo foo > $tmp/dir1/idirafter
 echo bar > $tmp/dir2/idirafter
-echo "#include \"idirafter\"" | $chibicc -I$tmp/dir1 -I$tmp/dir2 -E - | grep -q foo
+echo "#include \"idirafter\"" | $chibicc -I$tmp/dir1 -I$tmp/dir2 -E -xc - | grep -q foo
 check -idirafter
-echo "#include \"idirafter\"" | $chibicc -idirafter $tmp/dir1 -I$tmp/dir2 -E - | grep -q bar
+echo "#include \"idirafter\"" | $chibicc -idirafter $tmp/dir1 -I$tmp/dir2 -E -xc - | grep -q bar
 check -idirafter
 
 # -fcommon
-echo 'int foo;' | $chibicc -S -o- - | grep -q '\.comm foo'
+echo 'int foo;' | $chibicc -S -o- -xc - | grep -q '\.comm foo'
 check '-fcommon (default)'
 
-echo 'int foo;' | $chibicc -fcommon -S -o- - | grep -q '\.comm foo'
+echo 'int foo;' | $chibicc -fcommon -S -o- -xc - | grep -q '\.comm foo'
 check '-fcommon'
 
 # -fno-common
-echo 'int foo;' | $chibicc -fno-common -S -o- - | grep -q '^foo:'
+echo 'int foo;' | $chibicc -fno-common -S -o- -xc - | grep -q '^foo:'
 check '-fno-common'
 
 # -include
 echo foo > $tmp/out.h
-echo bar | $chibicc -include $tmp/out.h -E -o- - | grep -q -z 'foo.*bar'
+echo bar | $chibicc -include $tmp/out.h -E -o- -xc - | grep -q -z 'foo.*bar'
 check -include
-echo NULL | $chibicc -Iinclude -include stdio.h -E -o- - | grep -q 0
+echo NULL | $chibicc -Iinclude -include stdio.h -E -o- -xc - | grep -q 0
 check -include
 
+# -x
+echo 'int x;' | $chibicc -c -xc -o $tmp/foo.o -
+check -xc
+echo 'x:' | $chibicc -c -x assembler -o $tmp/foo.o -
+check '-x assembler'
+
+echo 'int x;' > $tmp/foo.c
+$chibicc -c -x assembler -x none -o $tmp/foo.o $tmp/foo.c
+check '-x none'
+
 echo OK