diff --git a/libc/decl/errno_values.h b/libc/decl/errno_values.h
index cb093c0c..15e4b8a0 100644
--- a/libc/decl/errno_values.h
+++ b/libc/decl/errno_values.h
@@ -68,6 +68,7 @@
 #define ENETUNREACH 76
 #define ENOBUFS 77
 #define ENOMSG 78
+#define ENOPROTOOPT 79
 
 #define EOPNOTSUPP ENOTSUP
 
diff --git a/libc/strerror.cpp b/libc/strerror.cpp
index 12d8d05f..67bc627b 100644
--- a/libc/strerror.cpp
+++ b/libc/strerror.cpp
@@ -97,6 +97,7 @@ extern "C" const char* sortix_strerror(int errnum)
 	case ENETUNREACH: return "Network is unreachable";
 	case ENOBUFS: return "No buffer space available";
 	case ENOMSG: return "No message of the desired type";
+	case ENOPROTOOPT: return "Protocol not available";
 	default: return "Unknown error condition";
 	}
 }