diff --git a/Makefile b/Makefile
index d8119fc..828db69 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ CFLAGS=-Ilib83 -c -mz80 --std-sdcc2x --no-std-crt0 --reserve-regs-iy --opt-code-
 
 OBJS=_crt0.rel clrscr.rel putchar.rel puts.rel exit.rel gotoxy.rel __assert_fail.rel \
      getchar.rel put_int.rel ctype.rel memcpy.rel memset.rel memmove.rel memcmp.rel \
-	 strcpy.rel \
+	 strcpy.rel strlen.rel \
 	 main.rel
 
 .PHONY: all clean try
diff --git a/lib83/strlen.c b/lib83/strlen.c
new file mode 100644
index 0000000..e377498
--- /dev/null
+++ b/lib83/strlen.c
@@ -0,0 +1,9 @@
+
+#include <string.h>
+
+size_t strlen (const char * str) {
+    register size_t i = 0;
+    while(*str++) i++;
+    return i;
+}
+