diff --git a/stm/std.h b/stm/std.h
index 41f477d26b..a2bf706176 100644
--- a/stm/std.h
+++ b/stm/std.h
@@ -13,7 +13,6 @@ void *memset(void *s, int c, size_t n);
 size_t strlen(const char *str);
 int strcmp(const char *s1, const char *s2);
 int strncmp(const char *s1, const char *s2, size_t n);
-char *strndup(const char *s, size_t n);
 char *strcpy(char *dest, const char *src);
 char *strcat(char *dest, const char *src);
 char *strchr(const char *s, int c);
diff --git a/stm/string0.c b/stm/string0.c
index 79fd4cc097..61350bd972 100644
--- a/stm/string0.c
+++ b/stm/string0.c
@@ -78,17 +78,6 @@ int strncmp(const char *s1, const char *s2, size_t n) {
     else return 0;
 }
 
-char *strndup(const char *s, size_t n) {
-    size_t len = strlen(s);
-    if (n > len) {
-        n = len;
-    }
-    char *s2 = malloc(n + 1);
-    memcpy(s2, s, n);
-    s2[n] = '\0';
-    return s2;
-}
-
 char *strcpy(char *dest, const char *src) {
     char *d = dest;
     while (*src) {
diff --git a/teensy/std.h b/teensy/std.h
index 6b768e7c8d..7003e7be0b 100644
--- a/teensy/std.h
+++ b/teensy/std.h
@@ -13,7 +13,6 @@ void *memset(void *s, int c, size_t n);
 int strlen(const char *str);
 int strcmp(const char *s1, const char *s2);
 int strncmp(const char *s1, const char *s2, size_t n);
-char *strndup(const char *s, size_t n);
 char *strcpy(char *dest, const char *src);
 char *strcat(char *dest, const char *src);