diff --git a/libc/decl/errno_values.h b/libc/decl/errno_values.h
index 3f6866e1..ecf71313 100644
--- a/libc/decl/errno_values.h
+++ b/libc/decl/errno_values.h
@@ -72,6 +72,7 @@
 #define ENOTCONN 80
 #define EDEADLK 81
 #define ENFILE 82
+#define EPROTOTYPE 83
 
 #define EOPNOTSUPP ENOTSUP
 
diff --git a/libc/strerror.cpp b/libc/strerror.cpp
index 98bff118..d718e7a0 100644
--- a/libc/strerror.cpp
+++ b/libc/strerror.cpp
@@ -101,6 +101,7 @@ extern "C" const char* sortix_strerror(int errnum)
 	case ENOTCONN: return "Socket is not connected";
 	case EDEADLK: return "Resource deadlock avoided";
 	case ENFILE: return "Too many open files in system";
+	case EPROTOTYPE: return "Wrong protocol type for socket";
 	default: return "Unknown error condition";
 	}
 }