diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index 3d43a428..40428c03 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -29,18 +29,28 @@ extern "C" {
 #endif
 
 #include <stddef.h>
-#include <stdbool.h>
 #include <limits.h>
 #include <stdarg.h>
 
 #include <stdio.h>
-#include <assert.h>
-#include <string.h>
-#include <stdlib.h>
-#include <ctype.h>
+
+#if __STDC_VERSION__ >= 199901L
+# include <stdbool.h>
+#else
+# define bool char
+# define true 1
+# define false 0
+#endif
+
+#if __STDC_VERSION__ >= 199901L
+# include <stddef.h>
+#elif ! defined(offsetof)
+# define offsetof(s,m) ((size_t)&(((s *)NULL)->m))
+#endif
 
 #include "picrin/config.h"
 #include "picrin/util.h"
+#include "picrin/compat.h"
 
 #if PIC_ENABLE_FLOAT
 # include <math.h>
diff --git a/extlib/benz/include/picrin/compat.h b/extlib/benz/include/picrin/compat.h
new file mode 100644
index 00000000..cca83d95
--- /dev/null
+++ b/extlib/benz/include/picrin/compat.h
@@ -0,0 +1,141 @@
+/**
+ * See Copyright Notice in picrin.h
+ */
+
+#ifndef PICRIN_COMPAT_H
+#define PICRIN_COMPAT_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#if PIC_ENABLE_LIBC
+
+#include <string.h>
+#include <ctype.h>
+#include <assert.h>
+#include <stdlib.h>
+
+#else
+
+# define assert(v) 0
+
+PIC_INLINE int
+isspace(int c)
+{
+  return c == ' ' || c == '\t' || c == '\r' || c == '\v' || c == '\f' || c == '\n';
+}
+
+PIC_INLINE int
+tolower(int c)
+{
+  return ('A' <= c && c <= 'Z') ? c - 'A' + 'a' : c;
+}
+
+PIC_INLINE int
+isdigit(int c)
+{
+  return '0' <= c && c <= '9';
+}
+
+PIC_INLINE char *
+strchr(const char *s, int c)
+{
+  do {
+    if (*s == c)
+      return (char *)s;
+  } while (*s++ != '\0');
+  return NULL;
+}
+
+PIC_INLINE size_t
+strlen(const char *s)
+{
+  size_t l = 0;
+
+  while (*s++) {
+    l++;
+  }
+  return l;
+}
+
+PIC_INLINE int
+strcmp(const char *s1, const char *s2)
+{
+  while (*s1 && *s1 == *s2) {
+    s1++;
+    s2++;
+  }
+  return (unsigned)*s1 - (unsigned)*s2;
+}
+
+PIC_INLINE long
+strtol(const char *nptr, char **endptr, int base)
+{
+  long l = 0;
+  char c;
+  int n;
+
+  while (1) {
+    c = *nptr;
+    if ('0' <= c && c <= '9')
+      n = c - '0';
+    else if ('a' <= c && c <= 'z')
+      n = c - 'a' + 10;
+    else if ('A' <= c && c <= 'Z')
+      n = c - 'A' + 10;
+    else
+      goto exit;
+
+    if (base <= n)
+      goto exit;
+
+    l = l * base + n;
+    nptr++;
+  }
+ exit:
+  if (endptr)
+    *endptr = (char *)nptr;
+  return l;
+}
+
+PIC_INLINE void *
+memset(void *s, int n, size_t c)
+{
+  char *p = s;
+
+  while (c-- > 0) {
+    *p++ = n;
+  }
+  return s;
+}
+
+PIC_INLINE void *
+memcpy(void *dst, const void *src, size_t n)
+{
+  const char *s = src;
+  char *d = dst;
+
+  while (n-- > 0) {
+    *d++ = *s++;
+  }
+  return d;
+}
+
+PIC_INLINE char *
+strcpy(char *dst, const char *src)
+{
+  char *d = dst;
+
+  while ((*dst++ = *src++) != 0);
+
+  return d;
+}
+
+#endif
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif
diff --git a/extlib/benz/include/picrin/config.h b/extlib/benz/include/picrin/config.h
index edf07594..58f5d54b 100644
--- a/extlib/benz/include/picrin/config.h
+++ b/extlib/benz/include/picrin/config.h
@@ -14,6 +14,9 @@
 /** enable floating point number support */
 /* #define PIC_ENABLE_FLOAT 1 */
 
+/** no dependency on libc */
+/* #define PIC_ENABLE_LIBC 1 */
+
 /** treat false value as none */
 /* #define PIC_NONE_IS_FALSE 1 */
 
@@ -82,6 +85,10 @@
 # endif
 #endif
 
+#ifndef PIC_ENABLE_LIBC
+# define PIC_ENABLE_LIBC 1
+#endif
+
 #if PIC_NAN_BOXING && defined(PIC_ENABLE_FLOAT) && ! PIC_ENABLE_FLOAT
 # error cannot disable float support when nan boxing is on
 #endif
diff --git a/extlib/benz/vm.c b/extlib/benz/vm.c
index 130084cd..fa07c6d2 100644
--- a/extlib/benz/vm.c
+++ b/extlib/benz/vm.c
@@ -255,10 +255,12 @@ pic_get_args(pic_state *pic, const char *format, ...)
 
       cstr = va_arg(ap, const char **);
       v = GET_OPERAND(pic,i);
-      if (! pic_str_p(v)) {
+      if (pic_str_p(v)) {
+        *cstr = pic_str_cstr(pic, pic_str_ptr(v));
+      }
+      else {
         pic_errorf(pic, "pic_get_args: expected string, but got ~s", v);
       }
-      *cstr = pic_str_cstr(pic, pic_str_ptr(v));
       break;
     }
     case 'm': {