diff --git a/contrib/linux-agent-installer/Icinga2Agent.bash b/contrib/linux-agent-installer/Icinga2Agent.bash
index e6a83e947..228fd190c 100644
--- a/contrib/linux-agent-installer/Icinga2Agent.bash
+++ b/contrib/linux-agent-installer/Icinga2Agent.bash
@@ -109,7 +109,7 @@ redhat)
 esac
 
 icinga_version() {
-  "$ICINGA2_BIN" --version 2>/dev/null | grep -oP '\(version: [rv]?\K\d+\.\d+\.\d+[^\)]*'
+  "$ICINGA2_BIN" --version 2>/dev/null | grep -oPi '\(version: [rv]?\K\d+\.\d+\.\d+[^\)]*'
 }
 
 version() {