diff --git a/README.md b/README.md
index cc2a9a6..783e1d8 100644
--- a/README.md
+++ b/README.md
@@ -79,6 +79,7 @@ zero). Work-in-progress APIs can change at any time.
     * [Example: vsnprintf](/examples/printf_str_va.c)
 * libc replacement (*work in progress*)
   * [ctype.h](/libc/include/ctype.h)
+  * [errno.h](/libc/include/errno.h)
   * [inttypes.h](/libc/include/inttypes.h)
   * [setjmp.h](/libc/include/setjmp.h)
   * [stdlib.h](/libc/include/stdlib.h)
diff --git a/libc/Makefile.am b/libc/Makefile.am
index d645adc..acdfa47 100644
--- a/libc/Makefile.am
+++ b/libc/Makefile.am
@@ -10,6 +10,7 @@ endif
 
 libc_la_SOURCES = \
 	src/ctype.c \
+	src/errno.c \
 	src/stdlib.c \
 	src/string.c
 
diff --git a/libc/include/Makefile.am b/libc/include/Makefile.am
index 056f416..3a76e8c 100644
--- a/libc/include/Makefile.am
+++ b/libc/include/Makefile.am
@@ -1,5 +1,6 @@
 nobase_include_HEADERS = \
 	ctype.h \
+	errno.h \
 	inttypes.h \
 	setjmp.h \
 	stdlib.h \
diff --git a/libc/include/errno.h b/libc/include/errno.h
new file mode 100644
index 0000000..755a4c7
--- /dev/null
+++ b/libc/include/errno.h
@@ -0,0 +1,16 @@
+#ifndef _ERRNO_H
+#define _ERRNO_H 1
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define ERANGE 1
+
+extern int errno;
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/libc/src/errno.c b/libc/src/errno.c
new file mode 100644
index 0000000..ebd7d69
--- /dev/null
+++ b/libc/src/errno.c
@@ -0,0 +1,7 @@
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <errno.h>
+
+int errno = 0;