diff --git a/libc/include/errno.h b/libc/include/errno.h
index 34052c3f..bdca7799 100644
--- a/libc/include/errno.h
+++ b/libc/include/errno.h
@@ -8,6 +8,7 @@
 #define EISDIR 4
 #define ENOENT 5
 #define EIO 6
+#define ENOTSUP 7
 
 __BEGIN_DECLS
 
diff --git a/libc/string/strerror.cpp b/libc/string/strerror.cpp
index 6a681478..6b337a8b 100644
--- a/libc/string/strerror.cpp
+++ b/libc/string/strerror.cpp
@@ -28,6 +28,9 @@ char* strerror(int error)
 	case EIO:
 		strcpy(buffer, "Input/output error");
 		break;
+	case ENOTSUP:
+		strcpy(buffer, "Operation not supported");
+		break;
 	default:
 		{
 			// FIXME: sprintf