diff --git a/libc/decl/errno_values.h b/libc/decl/errno_values.h
index e6c73910..4355c7dd 100644
--- a/libc/decl/errno_values.h
+++ b/libc/decl/errno_values.h
@@ -47,6 +47,7 @@
 #define ENXIO 55
 #define EPROTONOSUPPORT 56
 #define EAFNOSUPPORT 57
+#define ENOTSOCK 58
 
 #define EOPNOTSUPP ENOTSUP
 
diff --git a/libc/strerror.cpp b/libc/strerror.cpp
index f99f4cc3..3f4982f1 100644
--- a/libc/strerror.cpp
+++ b/libc/strerror.cpp
@@ -76,6 +76,7 @@ extern "C" const char* sortix_strerror(int errnum)
 	case ENXIO: return "No such device or address";
 	case EPROTONOSUPPORT: return "Protocol not supported";
 	case EAFNOSUPPORT: return "Address family not supported";
+	case ENOTSOCK: return "Not a socket";
 	default: return "Unknown error condition";
 	}
 }