diff --git a/libc/ctype.cpp b/libc/ctype.cpp
index db096439..67744fa4 100644
--- a/libc/ctype.cpp
+++ b/libc/ctype.cpp
@@ -64,3 +64,17 @@ int isxdigit(int c)
 {
 	return isdigit(c) || ('a' <= c && c <= 'f') || ('A' <= c && c <= 'F');
 }
+
+int toupper(int c)
+{
+	if (!islower(c))
+		return c;
+	return 'A' + (c - 'a');
+}
+
+int tolower(int c)
+{
+	if (!isupper(c))
+		return c;
+	return 'a' + (c - 'A');
+}
diff --git a/libc/include/ctype.h b/libc/include/ctype.h
index d2672fae..e569165c 100644
--- a/libc/include/ctype.h
+++ b/libc/include/ctype.h
@@ -18,4 +18,7 @@ int isspace(int);
 int isupper(int);
 int isxdigit(int);
 
+int toupper(int);
+int tolower(int);
+
 __END_DECLS
\ No newline at end of file