diff --git a/internal/pmtud/tcp/mss.go b/internal/pmtud/tcp/mss.go
index a8abe208..ea9b751b 100644
--- a/internal/pmtud/tcp/mss.go
+++ b/internal/pmtud/tcp/mss.go
@@ -12,6 +12,8 @@ import (
 	"github.com/qdm12/gluetun/internal/pmtud/ip"
 )
 
+var errTCPServersUnreachable = errors.New("all TCP servers are unreachable")
+
 // findHighestMSSDestination finds the destination with the highest
 // MSS amongst the provided destinations.
 func findHighestMSSDestination(ctx context.Context, familyToFD map[int]fileDescriptor,
@@ -65,6 +67,10 @@ func findHighestMSSDestination(ctx context.Context, familyToFD map[int]fileDescr
 		}
 	}
 
+	if mss == 0 { // no MSS found for any destination
+		return netip.AddrPort{}, 0, fmt.Errorf("%w (%d servers)", errTCPServersUnreachable, len(dsts))
+	}
+
 	maxPossibleMTU = ip.HeaderLength(dst.Addr().Is4()) + constants.BaseTCPHeaderLength + mss
 	logger.Debugf("server %s has the highest MSS %d allowing to test the MTU up to %d",
 		dst, mss, maxPossibleMTU)