diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4be5096..945fae2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -140,6 +140,7 @@ set(SOURCES
   src/libc/string/strchrnul.c
   src/libc/string/strcmp.c
   src/libc/string/strcpy.c
+  src/libc/string/strcspn.c
   src/libc/string/strdup.c
   src/libc/string/strerror.c
   src/libc/string/strlen.c
@@ -148,7 +149,8 @@ set(SOURCES
   src/libc/string/strncpy.c
   src/libc/string/strndup.c
   src/libc/string/strnlen.c
-  src/libc/string/strrchr.c)
+  src/libc/string/strrchr.c
+  src/libc/string/strspn.c)
 
 if(vhex-generic IN_LIST TARGET_FOLDERS)
   # TODO
diff --git a/STATUS b/STATUS
index ee805ca..dbbc4bd 100644
--- a/STATUS
+++ b/STATUS
@@ -122,10 +122,10 @@ DONE:       Function/symbol/macro is defined, builds, links, and is tested
 !    7.21.4.5  strxfrm: TODO
      7.21.5.1  memchr: DONE
      7.21.5.2  strchr: DONE
-!    7.21.5.3  strcspn: TODO
+     7.21.5.3  strcspn: DONE
 !    7.21.5.4  strpbrk: TODO
      7.21.5.5  strrchr: DONE
-!    7.21.5.6  strspn: TODO
+     7.21.5.6  strspn: DONE
 !    7.21.5.7  strstr: TODO
 !    7.21.5.8  strtok: TODO
      7.21.6.1  memset: DONE
diff --git a/include/string.h b/include/string.h
index 1cd8f35..3b3eab0 100644
--- a/include/string.h
+++ b/include/string.h
@@ -54,7 +54,7 @@ extern void *memchr(void const *__s, int __c, size_t __n);
 extern char *strchr(char const *__s, int __c);
 
 /* Count initial characters of __s that are not in __exclude. */
-extern char *strcspn(char const *__s, char const *__exclude);
+extern size_t strcspn(char const *__s, char const *__exclude);
 
 /* Find the first character of __s that is also in __include. */
 extern char *strpbrk(char const *__s, char const *__include);
@@ -63,7 +63,7 @@ extern char *strpbrk(char const *__s, char const *__include);
 extern char *strrchr(char const *__s, int __c);
 
 /* Count initial characters of __s that are in __include. */
-extern char *strspn(char const *__s, char const *__include);
+extern size_t strspn(char const *__s, char const *__include);
 
 /* Find the first occurrence of __s2 as a substring of __s1. */
 extern char *strstr(char const *__s1, char const *__s2);
diff --git a/src/libc/string/strcspn.c b/src/libc/string/strcspn.c
new file mode 100644
index 0000000..2a43612
--- /dev/null
+++ b/src/libc/string/strcspn.c
@@ -0,0 +1,8 @@
+#include <string.h>
+
+size_t strcspn(char const *s, char const *reject)
+{
+	size_t i = 0;
+	while(s[i] && !strchr(reject, s[i])) i++;
+	return i;
+}
diff --git a/src/libc/string/strspn.c b/src/libc/string/strspn.c
new file mode 100644
index 0000000..67fb58f
--- /dev/null
+++ b/src/libc/string/strspn.c
@@ -0,0 +1,8 @@
+#include <string.h>
+
+size_t strspn(char const *s, char const *accept)
+{
+	size_t i = 0;
+	while(s[i] && strchr(accept, s[i])) i++;
+	return i;
+}