diff --git a/confmap/resolver.go b/confmap/resolver.go
index fe31f75b77..8276c818f7 100644
--- a/confmap/resolver.go
+++ b/confmap/resolver.go
@@ -209,17 +209,20 @@ func (mr *Resolver) expandValueRecursively(ctx context.Context, value interface{
 	return nil, errors.New("too many recursive expansions")
 }
 
+// Scheme name consist of a sequence of characters beginning with a letter and followed by any
+// combination of letters, digits, plus ("+"), period ("."), or hyphen ("-").
+var expandRegexp = regexp.MustCompile(`^\$\{[A-Za-z][A-Za-z0-9+.-]+:.*}$`)
+
 func (mr *Resolver) expandValue(ctx context.Context, value interface{}) (interface{}, bool, error) {
 	switch v := value.(type) {
 	case string:
 		// If it doesn't have the format "${scheme:opaque}" no need to expand.
-		if !strings.HasPrefix(v, "${") || !strings.HasSuffix(v, "}") {
+		if !expandRegexp.MatchString(v) {
 			return value, false, nil
 		}
 		uri := v[2 : len(v)-1]
-		// For backwards compatibility:
-		// - empty scheme means "env".
-		ret, err := mr.retrieveValue(ctx, location{uri: uri, defaultScheme: "env"})
+		// At this point it is guaranteed to have a valid "scheme" based on the expandRegexp, so no default.
+		ret, err := mr.retrieveValue(ctx, location{uri: uri})
 		if err != nil {
 			return nil, false, err
 		}
diff --git a/confmap/resolver_test.go b/confmap/resolver_test.go
index a9a6df771a..6e4572d864 100644
--- a/confmap/resolver_test.go
+++ b/confmap/resolver_test.go
@@ -321,7 +321,6 @@ func TestResolverExpandEnvVars(t *testing.T) {
 		{name: "expand-with-no-env.yaml"},
 		{name: "expand-with-partial-env.yaml"},
 		{name: "expand-with-all-env.yaml"},
-		{name: "expand-with-all-env-with-source.yaml"},
 	}
 
 	envs := map[string]string{
@@ -355,6 +354,27 @@ func TestResolverExpandEnvVars(t *testing.T) {
 	}
 }
 
+func TestResolverDoneNotExpandOldEnvVars(t *testing.T) {
+	expectedCfgMap := map[string]interface{}{"test.1": "${EXTRA}", "test.2": "$EXTRA"}
+	fileProvider := newFakeProvider("test", func(_ context.Context, uri string, _ WatcherFunc) (Retrieved, error) {
+		return NewRetrieved(expectedCfgMap)
+	})
+	envProvider := newFakeProvider("env", func(_ context.Context, uri string, _ WatcherFunc) (Retrieved, error) {
+		return NewRetrieved("some string")
+	})
+	emptySchemeProvider := newFakeProvider("", func(_ context.Context, uri string, _ WatcherFunc) (Retrieved, error) {
+		return NewRetrieved("some string")
+	})
+
+	resolver, err := NewResolver(ResolverSettings{URIs: []string{"test:"}, Providers: makeMapProvidersMap(fileProvider, envProvider, emptySchemeProvider), Converters: nil})
+	require.NoError(t, err)
+	resolver.enableExpand = true
+	// Test that expanded configs are the same with the simple config with no env vars.
+	cfgMap, err := resolver.Resolve(context.Background())
+	require.NoError(t, err)
+	assert.Equal(t, expectedCfgMap, cfgMap.ToStringMap())
+}
+
 func TestResolverExpandMapAndSliceValues(t *testing.T) {
 	provider := newFakeProvider("input", func(context.Context, string, WatcherFunc) (*Retrieved, error) {
 		return NewRetrieved(map[string]interface{}{
diff --git a/confmap/testdata/expand-with-all-env-with-source.yaml b/confmap/testdata/expand-with-all-env-with-source.yaml
deleted file mode 100644
index 5386e05158..0000000000
--- a/confmap/testdata/expand-with-all-env-with-source.yaml
+++ /dev/null
@@ -1,11 +0,0 @@
-test_map:
-  extra: "${env:EXTRA}"
-  extra_map:
-    recv.1: "${env:EXTRA_MAP_VALUE_1}"
-    recv.2: "${env:EXTRA_MAP_VALUE_2}"
-  extra_list_map:
-    - { recv.1: "${env:EXTRA_LIST_MAP_VALUE_1}",recv.2: "${env:EXTRA_LIST_MAP_VALUE_2}" }
-  extra_list:
-    - "${env:EXTRA_LIST_VALUE_1}"
-    - "${env:EXTRA_LIST_VALUE_2}"
-    
diff --git a/confmap/testdata/expand-with-all-env.yaml b/confmap/testdata/expand-with-all-env.yaml
index ed623bf9a5..5386e05158 100644
--- a/confmap/testdata/expand-with-all-env.yaml
+++ b/confmap/testdata/expand-with-all-env.yaml
@@ -1,11 +1,11 @@
 test_map:
-  extra: "${EXTRA}"
+  extra: "${env:EXTRA}"
   extra_map:
-    recv.1: "${EXTRA_MAP_VALUE_1}"
-    recv.2: "${EXTRA_MAP_VALUE_2}"
+    recv.1: "${env:EXTRA_MAP_VALUE_1}"
+    recv.2: "${env:EXTRA_MAP_VALUE_2}"
   extra_list_map:
-    - { recv.1: "${EXTRA_LIST_MAP_VALUE_1}",recv.2: "${EXTRA_LIST_MAP_VALUE_2}" }
+    - { recv.1: "${env:EXTRA_LIST_MAP_VALUE_1}",recv.2: "${env:EXTRA_LIST_MAP_VALUE_2}" }
   extra_list:
-    - "${EXTRA_LIST_VALUE_1}"
-    - "${EXTRA_LIST_VALUE_2}"
+    - "${env:EXTRA_LIST_VALUE_1}"
+    - "${env:EXTRA_LIST_VALUE_2}"
     
diff --git a/confmap/testdata/expand-with-partial-env.yaml b/confmap/testdata/expand-with-partial-env.yaml
index fb8ffe51b8..d995c36fa0 100644
--- a/confmap/testdata/expand-with-partial-env.yaml
+++ b/confmap/testdata/expand-with-partial-env.yaml
@@ -1,10 +1,10 @@
 test_map:
-  extra: "${EXTRA}"
+  extra: "${env:EXTRA}"
   extra_map:
-    recv.1: "${EXTRA_MAP_VALUE_1}"
+    recv.1: "${env:EXTRA_MAP_VALUE_1}"
     recv.2: "some map value_2"
   extra_list_map:
-    - { recv.1: "some list map value_1",recv.2: "${EXTRA_LIST_MAP_VALUE_2}" }
+    - { recv.1: "some list map value_1",recv.2: "${env:EXTRA_LIST_MAP_VALUE_2}" }
   extra_list:
     - "some list value_1"
-    - "${EXTRA_LIST_VALUE_2}"
+    - "${env:EXTRA_LIST_VALUE_2}"