diff --git a/agent/disk.go b/agent/disk.go
index 13bb1b1ce..8574beff0 100644
--- a/agent/disk.go
+++ b/agent/disk.go
@@ -204,7 +204,10 @@ func isRootFallbackPartition(p disk.PartitionStat, rootMountPoint string) bool {
 // partition looks like the active root mount but still needs translating to an
 // I/O device key.
 func (d *diskDiscovery) addPartitionRootFs(device, mountpoint string) bool {
-	fs, match := findIoDevice(filepath.Base(device), d.ctx.diskIoCounters)
+	// device is passed through as-is: findIoDevice normalizes it, and
+	// filepath.Base would turn a Windows volume name such as "C:" into "\"
+	// on the way in (#2417).
+	fs, match := findIoDevice(device, d.ctx.diskIoCounters)
 	if !match {
 		return false
 	}
@@ -527,13 +530,45 @@ func filesystemMatchesPartitionSetting(filesystem string, p disk.PartitionStat)
 
 // normalizeDeviceName canonicalizes device strings for comparisons.
 func normalizeDeviceName(value string) string {
-	name := filepath.Base(strings.TrimSpace(value))
+	name := strings.TrimSpace(value)
+	if volume, ok := windowsVolumeName(name); ok {
+		return volume
+	}
+	name = filepath.Base(name)
 	if name == "." {
 		return ""
 	}
 	return name
 }
 
+// windowsVolumeName returns the canonical form of a bare Windows volume
+// specifier, so that "C:", `C:\` and "C:/" all name the same drive.
+//
+// filepath.Base cannot do this. On Windows it treats "C:" as a volume name
+// with no path element to take the base of and returns "\", so every drive
+// letter normalizes to the same key. findIoDevice then returns whichever
+// counter the map happened to yield first, which registers the root
+// filesystem under a random drive (#2417).
+func windowsVolumeName(value string) (string, bool) {
+	if len(value) < 2 || value[1] != ':' {
+		return "", false
+	}
+	if c := value[0]; !('a' <= c && c <= 'z' || 'A' <= c && c <= 'Z') {
+		return "", false
+	}
+	if len(value) == 2 {
+		return value, true
+	}
+	// Only separators may follow the specifier. "C:data" is a drive-relative
+	// path, not a volume.
+	for i := 2; i < len(value); i++ {
+		if value[i] != '\\' && value[i] != '/' {
+			return "", false
+		}
+	}
+	return value[:2], true
+}
+
 // Sets start values for disk I/O stats.
 func (a *Agent) initializeDiskIoStats(diskIoCounters map[string]disk.IOCountersStat) {
 	a.fsNames = a.fsNames[:0]
diff --git a/agent/disk_test.go b/agent/disk_test.go
index 70fa2083b..59f423bfd 100644
--- a/agent/disk_test.go
+++ b/agent/disk_test.go
@@ -1057,3 +1057,70 @@ func TestIoTimeDelta(t *testing.T) {
 
 	assert.Equal(t, uint64(0), ioTimeDelta(200, math.MaxUint32+1000))
 }
+
+func TestNormalizeDeviceName(t *testing.T) {
+	// A Windows volume name is not a path element, so every spelling of the
+	// same drive has to normalize to the same key. filepath.Base cannot do
+	// this: on Windows it strips the "C:" specifier and returns "\", which
+	// collapses every drive letter onto one key (#2417).
+	for _, spelling := range []string{"C:", `C:\`, "C:/", `C:\\`} {
+		assert.Equal(t, "C:", normalizeDeviceName(spelling), "spelling %q", spelling)
+	}
+	// Case is left to the caller, as it already is for Linux device names.
+	assert.Equal(t, "d:", normalizeDeviceName("d:"))
+	assert.Equal(t, "c:", normalizeDeviceName(" c: "))
+
+	// Non-volume inputs keep using filepath.Base.
+	assert.Equal(t, "sda1", normalizeDeviceName("/dev/sda1"))
+	assert.Equal(t, "sda1", normalizeDeviceName("/dev/sda1/"))
+	assert.Equal(t, "nvme0n1p2", normalizeDeviceName("  /dev/nvme0n1p2  "))
+	assert.Equal(t, "", normalizeDeviceName("."))
+	assert.Equal(t, "", normalizeDeviceName("   "))
+
+	// A drive-relative path is a path, not a volume.
+	assert.Equal(t, `C:data`, normalizeDeviceName(`C:data`))
+}
+
+func TestFindIoDeviceWindowsVolumeNames(t *testing.T) {
+	// Every drive normalizes to a distinct key, so the root drive resolves
+	// exactly instead of to whichever counter the map yielded first (#2417).
+	ioCounters := map[string]disk.IOCountersStat{
+		"C:": {Name: "C:", ReadBytes: 10, WriteBytes: 10},
+		"D:": {Name: "D:", ReadBytes: 20, WriteBytes: 20},
+		"P:": {Name: "P:", ReadBytes: 30, WriteBytes: 30},
+	}
+
+	for i := 0; i < 32; i++ {
+		device, ok := findIoDevice("C:", ioCounters)
+		assert.True(t, ok)
+		assert.Equal(t, "C:", device)
+	}
+
+	// The drive may arrive with a trailing separator, as a mount point does.
+	device, ok := findIoDevice(`C:\`, ioCounters)
+	assert.True(t, ok)
+	assert.Equal(t, "C:", device)
+}
+
+func TestAddPartitionRootFsWindowsDrive(t *testing.T) {
+	agent := &Agent{fsStats: make(map[string]*system.FsStats)}
+	discovery := diskDiscovery{
+		agent: agent,
+		ctx: fsRegistrationContext{
+			isWindows: true,
+			diskIoCounters: map[string]disk.IOCountersStat{
+				"C:": {Name: "C:"},
+				"D:": {Name: "D:"},
+				"P:": {Name: "P:"},
+			},
+		},
+	}
+
+	ok := discovery.addPartitionRootFs("C:", `C:\`)
+
+	assert.True(t, ok)
+	assert.Len(t, agent.fsStats, 1)
+	stats, exists := agent.fsStats["C:"]
+	assert.True(t, exists)
+	assert.True(t, stats.Root)
+}