Index: usr.sbin/prometheus_sysctl_exporter/prometheus_sysctl_exporter.c
===================================================================
--- usr.sbin/prometheus_sysctl_exporter/prometheus_sysctl_exporter.c
+++ usr.sbin/prometheus_sysctl_exporter/prometheus_sysctl_exporter.c
@@ -396,6 +396,9 @@
 				snprintf(buf, sizeof(buf), "%c",
 				    isalnum(*name) ? *name : '_');
 				strlcat(metric, buf, mlen);
+				if (*name == '_') {
+					strlcat(metric, buf, mlen);
+				}
 				++name;
 			}
 		}