diff --git a/inc/string.h b/inc/string.h
index b0e13d7..1d89803 100644
--- a/inc/string.h
+++ b/inc/string.h
@@ -7,19 +7,23 @@
 #include <stddef.h>
 
 #if !defined(NULL)
-#define NULL ((void *)0)
+    #define NULL ((void *)0)
 #endif
 
 #if !defined(__STDC_LIB_EXT1__)
-#define __STDC_LIB_EXT1__
-typedef int errno_t;
-typedef size_t rsize_t;
+    #define __STDC_LIB_EXT1__
+    typedef int errno_t;
+    typedef size_t rsize_t;
 #endif
 
 #if __STDC_WANT_SECURE_LIB__ == 1
-#if !defined(__STDC_WANT_LIB_EXT1__)
-#define __STDC_WANT_LIB_EXT1__ 1
+    #if !defined(__STDC_WANT_LIB_EXT1__)
+        #define __STDC_WANT_LIB_EXT1__ 1
+    #endif
 #endif
+
+#if !defined(__STDC_ALLOC_LIB__)
+    #define __STDC_ALLOC_LIB__
 #endif
 
 // int _wcsicmp(const wchar_t *string1, const wchar_t *string2);
@@ -50,7 +54,9 @@ size_t strlen(const char *s);
 // Linux extension: reentrant strtok
 char *strtok_r(char *restrict s1, const char *restrict s2, char **restrict ctx);
 
+// Extension 1
 #if __STDC_WANT_LIB_EXT1__ == 1
+
 errno_t memcpy_s(void *restrict s1, rsize_t s1max, const void *restrict s2, rsize_t n);
 errno_t memmove_s(void *s1, rsize_t s1max, const void *s2, rsize_t n);
 errno_t strcpy_s(char *restrict s1, rsize_t s1max, const char *restrict s2);
@@ -62,4 +68,12 @@ errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n);
 errno_t strerror_s(char *s, rsize_t maxsize, errno_t errnum);
 size_t strerrorlen_s(errno_t errnum);
 size_t strnlen_s(const char *str, size_t strsz);
+
+#endif
+
+// Extension 2
+#if __STDC_WANT_LIB_EXT2__ == 1
+
+char *strdup(const char *str1);
+
 #endif
diff --git a/src/code/string.c b/src/code/string.c
index d3197a0..69798cb 100644
--- a/src/code/string.c
+++ b/src/code/string.c
@@ -236,3 +236,10 @@ size_t strnlen_s(const char *s, size_t maxsize) {
     }
     return i;
 }
+
+char *strdup(const char *str1) {
+    size_t len = strlen(str1);
+    char *copy = calloc(len+1, 1);
+    strcpy(copy, str1);
+    return copy;
+}