diff --git a/include/termios.h b/include/termios.h
index 14cb8f656d..00ff32e5c6 100644
--- a/include/termios.h
+++ b/include/termios.h
@@ -298,9 +298,6 @@ int tcsendbreak(int fd, int duration);
 
 int tcsetattr(int fd, int options, FAR const struct termios *termiosp);
 
-/* Check if a file descriptor corresponds to a terminal I/O file */
-
-int isatty(int fd);
 
 #undef EXTERN
 #ifdef __cplusplus
diff --git a/include/unistd.h b/include/unistd.h
index 909df0b338..7361b412ea 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -165,6 +165,10 @@ ssize_t write(int fd, FAR const void *buf, size_t nbytes);
 ssize_t pread(int fd, FAR void *buf, size_t nbytes, off_t offset);
 ssize_t pwrite(int fd, FAR const void *buf, size_t nbytes, off_t offset);
 
+/* Check if a file descriptor corresponds to a terminal I/O file */
+
+int     isatty(int fd);
+
 /* Memory management */
 
 #if defined(CONFIG_ARCH_ADDRENV) && defined(CONFIG_MM_PGALLOC) && \