diff --git a/test/testutil/ports.go b/test/testutil/ports.go
index 867f20761..103f5a440 100644
--- a/test/testutil/ports.go
+++ b/test/testutil/ports.go
@@ -11,6 +11,23 @@ import (
 // GrpcPortOffset is the offset weed mini uses to derive gRPC ports from HTTP ports.
 const GrpcPortOffset = 10000
 
+// linuxEphemeralPortFloor is the Linux default ip_local_port_range lower bound.
+// Ports at or above it can be claimed as the source port of a transient
+// outbound connection during mini's own startup (e.g. volume dialing master
+// gRPC) in the window between allocation and the listener bind, surfacing as
+// "bind: address already in use".
+const linuxEphemeralPortFloor = 32768
+
+// miniPortMin/miniPortMax bound the random HTTP port range for weed mini.
+// The cap keeps both the HTTP port and its +GrpcPortOffset gRPC counterpart
+// below linuxEphemeralPortFloor, out of the range the kernel draws ephemeral
+// source ports from, so the steal above cannot happen. Deriving the cap from
+// GrpcPortOffset keeps the two in lockstep if the offset ever changes.
+const (
+	miniPortMin = 10000
+	miniPortMax = linuxEphemeralPortFloor - GrpcPortOffset
+)
+
 // miniDefaultPorts are the weed mini flag defaults (see weed/command/mini.go).
 // A test only overrides services it uses; unspecified services still bind
 // these defaults, so allocation must avoid handing them out (or any value
@@ -83,8 +100,8 @@ func MustAllocatePorts(t *testing.T, count int) []int {
 // wrong port and hang.
 func AllocateMiniPorts(count int) ([]int, error) {
 	const (
-		minPort = 10000
-		maxPort = 55000
+		minPort = miniPortMin
+		maxPort = miniPortMax
 	)
 	reserved := reservedMiniPorts()
 	ports := make([]int, 0, count)
@@ -155,8 +172,8 @@ func MustFreeMiniPort(t *testing.T, name string) int {
 // allocated, so a mini gRPC port cannot be recycled as a regular port mid-batch.
 func AllocatePortSet(miniCount, regularCount int) (mini []int, regular []int, err error) {
 	const (
-		minPort = 10000
-		maxPort = 55000
+		minPort = miniPortMin
+		maxPort = miniPortMax
 	)
 	reserved := reservedMiniPorts()
 	mini = make([]int, 0, miniCount)
diff --git a/test/testutil/ports_test.go b/test/testutil/ports_test.go
index 5c02e20a3..8d22c51e7 100644
--- a/test/testutil/ports_test.go
+++ b/test/testutil/ports_test.go
@@ -25,6 +25,27 @@ func TestAllocateMiniPortsAvoidsMiniDefaults(t *testing.T) {
 	}
 }
 
+// AllocateMiniPorts must keep every port it hands out, and that port's gRPC
+// counterpart, below 32768 - the Linux default ip_local_port_range floor.
+// A real failure: filer was allocated 44204, then lost the bind to a transient
+// outbound connection that had grabbed 44204 as an ephemeral source port
+// during mini startup ("bind: address already in use").
+func TestAllocateMiniPortsBelowEphemeralFloor(t *testing.T) {
+	const ephemeralFloor = linuxEphemeralPortFloor
+	for iter := 0; iter < 200; iter++ {
+		ports, err := AllocateMiniPorts(4)
+		if err != nil {
+			t.Fatalf("iter %d: AllocateMiniPorts: %v", iter, err)
+		}
+		for _, p := range ports {
+			if p+GrpcPortOffset >= ephemeralFloor {
+				t.Fatalf("iter %d: port %d (gRPC %d) reaches the ephemeral range floor %d",
+					iter, p, p+GrpcPortOffset, ephemeralFloor)
+			}
+		}
+	}
+}
+
 func TestAllocatePortSetNoGrpcCollision(t *testing.T) {
 	// Run a few iterations to catch the OS-recycles-just-closed-port race
 	// that previously hit regular ports when the mini gRPC offset was freed