diff --git a/extra_tests/termios_test.expected b/extra_tests/termios_test.expected
new file mode 100644
index 0000000..ede3aff
--- /dev/null
+++ b/extra_tests/termios_test.expected
@@ -0,0 +1,8 @@
+stdin is a tty? 
+1
+stdout is a tty? 
+0
+stderr is a tty? 
+0
+Invalid fd (999) is a tty? 
+-1
diff --git a/extra_tests/termios_test.sl b/extra_tests/termios_test.sl
new file mode 100644
index 0000000..c9c50a6
--- /dev/null
+++ b/extra_tests/termios_test.sl
@@ -0,0 +1,16 @@
+import stdlib.sl
+import termios.sl
+
+word main
+    "stdin is a tty? " puts
+    0 isatty puti cr
+
+    "stdout is a tty? " puts
+    1 isatty puti cr
+
+    "stderr is a tty? " puts
+    2 isatty puti cr
+
+    "Invalid fd (999) is a tty? " puts
+    999 isatty puti cr
+end
diff --git a/stdlib/termios.sl b/stdlib/termios.sl
new file mode 100644
index 0000000..4f2b641
--- /dev/null
+++ b/stdlib/termios.sl
@@ -0,0 +1,36 @@
+import stdlib.sl
+
+macro TCGETS 0 0x5401 ;
+macro ENOTTY 0 25 ;
+macro EBADF 0 9 ;
+
+# isatty [* | fd] -> [* | flag]
+word isatty
+    >r                           # save fd
+
+    60 alloc                     # push addr
+    r@ TCGETS over 3 16 syscall  # addr result
+
+    # Duplicate result and save it
+    dup >r                       # push result to return stack
+
+    # Free buffer
+    60 swap free                 # free(addr, size)
+
+    # Restore result
+    r>                           # result back to data stack
+
+    # Check result
+    dup ENOTTY neg == if                # -ENOTTY (not a tty)
+        drop 0
+    else
+        dup EBADF neg == if             # -EBADF (bad fd)
+            drop -1
+        else
+            # Any other value means it's a tty
+            drop 1
+        end
+    end
+
+    rdrop
+end
diff --git a/test.py b/test.py
index 3ee45b0..b14c7b3 100644
--- a/test.py
+++ b/test.py
@@ -28,6 +28,7 @@ DEFAULT_EXTRA_TESTS = [
     "extra_tests/c_extern_structs.sl",
     "extra_tests/fn_test.sl",
     "extra_tests/nob_test.sl",
+    "extra_tests/termios_test.sl",
 ]
 
 COLORS = {