diff --git a/lib/services/matchers.go b/lib/services/matchers.go
index ad1d5ed3932..50ad74423cb 100644
--- a/lib/services/matchers.go
+++ b/lib/services/matchers.go
@@ -30,6 +30,7 @@ import (
 	"github.com/gravitational/teleport/api/types"
 	apiutils "github.com/gravitational/teleport/api/utils"
 	azureutils "github.com/gravitational/teleport/api/utils/azure"
+	libslices "github.com/gravitational/teleport/lib/utils/slices"
 	"github.com/gravitational/teleport/lib/utils/typical"
 )
 
@@ -82,7 +83,6 @@ func SimplifyAzureMatchers(matchers []types.AzureMatcher) []types.AzureMatcher {
 	for _, m := range matchers {
 		subs := apiutils.Deduplicate(m.Subscriptions)
 		groups := apiutils.Deduplicate(m.ResourceGroups)
-		regions := apiutils.Deduplicate(m.Regions)
 		ts := apiutils.Deduplicate(m.Types)
 		if len(subs) == 0 || slices.Contains(subs, types.Wildcard) {
 			subs = []string{types.Wildcard}
@@ -90,12 +90,13 @@ func SimplifyAzureMatchers(matchers []types.AzureMatcher) []types.AzureMatcher {
 		if len(groups) == 0 || slices.Contains(groups, types.Wildcard) {
 			groups = []string{types.Wildcard}
 		}
-		if len(regions) == 0 || slices.Contains(regions, types.Wildcard) {
+		var regions []string
+		if len(m.Regions) == 0 || slices.Contains(m.Regions, types.Wildcard) {
 			regions = []string{types.Wildcard}
 		} else {
-			for i, region := range regions {
-				regions[i] = azureutils.NormalizeLocation(region)
-			}
+			// Normalize before dedup so case-variant inputs ("East US", "eastus") collapse.
+			// The fresh slice also keeps m.Regions safe from the watcher's concurrent IsEqual reads.
+			regions = apiutils.Deduplicate(libslices.Map(m.Regions, azureutils.NormalizeLocation))
 		}
 		elem := m
 		elem.Subscriptions = subs
diff --git a/lib/services/matchers_test.go b/lib/services/matchers_test.go
index 40e01dc8241..48e2f036cf3 100644
--- a/lib/services/matchers_test.go
+++ b/lib/services/matchers_test.go
@@ -196,6 +196,77 @@ func TestSimplifyAzureMatchers(t *testing.T) {
 	require.Equal(t, want, simplified)
 }
 
+// TestSimplifyAzureMatchersDoesNotMutateInput guards against a regression where
+// SimplifyAzureMatchers normalized regions through an aliased input slice,
+// mutating the caller's matcher and racing with concurrent readers.
+func TestSimplifyAzureMatchersDoesNotMutateInput(t *testing.T) {
+	t.Parallel()
+	matchers := []types.AzureMatcher{
+		{
+			Subscriptions:  []string{"sub-1"},
+			ResourceGroups: []string{"rg-1"},
+			// "East US" normalizes to "eastus", so any in-place write is observable by value comparison.
+			Regions: []string{"East US"},
+			Types:   []string{"vm"},
+		},
+	}
+	regionsBackingArray := matchers[0].Regions
+
+	simplified := SimplifyAzureMatchers(matchers)
+
+	require.Equal(t, []string{"East US"}, matchers[0].Regions,
+		"input regions slice must not be mutated")
+	require.Equal(t, "East US", regionsBackingArray[0],
+		"input regions backing array must not be mutated")
+	require.Equal(t, []string{"eastus"}, simplified[0].Regions,
+		"output regions must be normalized")
+}
+
+// TestSimplifyAzureMatchersDeduplicatesNormalizedRegions guards against a
+// regression where deduplication ran before normalization, leaving case-variant
+// inputs like "East US" and "eastus" as distinct entries in the output.
+func TestSimplifyAzureMatchersDeduplicatesNormalizedRegions(t *testing.T) {
+	t.Parallel()
+	matchers := []types.AzureMatcher{
+		{
+			Subscriptions:  []string{"sub-1"},
+			ResourceGroups: []string{"rg-1"},
+			// Four inputs, three of which normalize to "eastus", one to "eastus2".
+			// Byte-equality dedup before normalization would let all four through.
+			Regions: []string{"East US", "eastus", "EASTUS", "East US 2"},
+			Types:   []string{"vm"},
+		},
+	}
+
+	simplified := SimplifyAzureMatchers(matchers)
+
+	require.ElementsMatch(t, []string{"eastus", "eastus2"}, simplified[0].Regions,
+		"case-variant regions must collapse to one normalized entry per location")
+}
+
+// TestSimplifyAzureMatchersCollapsesRegionsWildcard locks in the Regions
+// wildcard branch: when any region entry is the wildcard, the output must
+// collapse to a single wildcard rather than keep the explicit entries
+// alongside it. Without this test the wildcard collapse for Regions has no
+// fixture coverage (existing tests only exercise the wildcard branch via an
+// empty Regions slice).
+func TestSimplifyAzureMatchersCollapsesRegionsWildcard(t *testing.T) {
+	t.Parallel()
+	matchers := []types.AzureMatcher{
+		{
+			Subscriptions:  []string{"sub-1"},
+			ResourceGroups: []string{"rg-1"},
+			Regions:        []string{"East US", types.Wildcard, "westus"},
+			Types:          []string{"vm"},
+		},
+	}
+
+	simplified := SimplifyAzureMatchers(matchers)
+
+	require.Equal(t, []string{types.Wildcard}, simplified[0].Regions,
+		"any wildcard in regions must collapse the slice to a single wildcard")
+}
+
 func TestMatchResourceByFilters_Helper(t *testing.T) {
 	t.Parallel()
 
diff --git a/lib/srv/discovery/discovery.go b/lib/srv/discovery/discovery.go
index fb53efa32db..927cfcbbaf4 100644
--- a/lib/srv/discovery/discovery.go
+++ b/lib/srv/discovery/discovery.go
@@ -1590,7 +1590,7 @@ func (s *Server) startAzureServerDiscovery() {
 		// in case of API calls, e.g., to expand subscription wildcard.
 		dynamicConfigs := make(map[string][]types.AzureMatcher, len(s.dynamicDiscoveryConfig))
 		for _, config := range s.dynamicDiscoveryConfig {
-			dynamicConfigs[config.GetName()] = config.Spec.Azure
+			dynamicConfigs[config.GetName()] = services.SimplifyAzureMatchers(config.Spec.Azure)
 		}
 		s.dynamicDiscoveryConfigMu.RUnlock()