diff --git a/libc/decl/errno_values.h b/libc/decl/errno_values.h
index 239ac0b4..9e6e04cd 100644
--- a/libc/decl/errno_values.h
+++ b/libc/decl/errno_values.h
@@ -52,6 +52,7 @@
 #define ETIMEDOUT 60
 #define ECONNREFUSED 61
 #define EDOM 62
+#define EINPROGRESS 63
 
 #define EOPNOTSUPP ENOTSUP
 
diff --git a/libc/strerror.cpp b/libc/strerror.cpp
index 41b83787..bed16d4b 100644
--- a/libc/strerror.cpp
+++ b/libc/strerror.cpp
@@ -81,6 +81,7 @@ extern "C" const char* sortix_strerror(int errnum)
 	case ETIMEDOUT: return "Connection timed out";
 	case ECONNREFUSED: return "Connection refused";
 	case EDOM: return "Mathematics argument out of domain of function";
+	case EINPROGRESS: return "Operation in progress";
 	default: return "Unknown error condition";
 	}
 }