diff --git a/audio/common/7.0/types.hal b/audio/common/7.0/types.hal
index 99c2e5a..bea0705 100644
--- a/audio/common/7.0/types.hal
+++ b/audio/common/7.0/types.hal
@@ -61,6 +61,8 @@
  * Audio stream type describing the intended use case of a stream.
  * See 'audioStreamType' in audio_policy_configuration.xsd for the
  * list of allowed values.
+ *
+ * An empty string is used to specify the "default" stream type.
  */
 typedef string AudioStreamType;
 
diff --git a/audio/common/all-versions/default/7.0/HidlUtils.cpp b/audio/common/all-versions/default/7.0/HidlUtils.cpp
index bb3a596..2949fac 100644
--- a/audio/common/all-versions/default/7.0/HidlUtils.cpp
+++ b/audio/common/all-versions/default/7.0/HidlUtils.cpp
@@ -335,25 +335,35 @@
     return BAD_VALUE;
 }
 
+// The "default" value of audio_stream_type_t is represented by an empty string.
 status_t HidlUtils::audioStreamTypeFromHal(audio_stream_type_t halStreamType,
                                            AudioStreamType* streamType) {
-    *streamType = audio_stream_type_to_string(halStreamType);
-    if (!streamType->empty() && !xsd::isUnknownAudioStreamType(*streamType)) {
+    if (halStreamType != AUDIO_STREAM_DEFAULT) {
+        *streamType = audio_stream_type_to_string(halStreamType);
+        if (!streamType->empty() && !xsd::isUnknownAudioStreamType(*streamType)) {
+            return NO_ERROR;
+        }
+        ALOGE("Unknown audio stream type value 0x%X", halStreamType);
+        return BAD_VALUE;
+    } else {
+        *streamType = "";
         return NO_ERROR;
     }
-    ALOGE("Unknown audio stream type value 0x%X", halStreamType);
-    return BAD_VALUE;
 }
 
 status_t HidlUtils::audioStreamTypeToHal(const AudioStreamType& streamType,
                                          audio_stream_type_t* halStreamType) {
-    if (!xsd::isUnknownAudioStreamType(streamType) &&
-        audio_stream_type_from_string(streamType.c_str(), halStreamType)) {
+    if (!streamType.empty()) {
+        if (!xsd::isUnknownAudioStreamType(streamType) &&
+            audio_stream_type_from_string(streamType.c_str(), halStreamType)) {
+            return NO_ERROR;
+        }
+        ALOGE("Unknown audio stream type \"%s\"", streamType.c_str());
+        return BAD_VALUE;
+    } else {
+        *halStreamType = AUDIO_STREAM_DEFAULT;
         return NO_ERROR;
     }
-    ALOGE("Unknown audio stream type \"%s\"", streamType.c_str());
-    *halStreamType = AUDIO_STREAM_DEFAULT;
-    return BAD_VALUE;
 }
 
 status_t HidlUtils::audioConfigFromHal(const audio_config_t& halConfig, bool isInput,
diff --git a/audio/common/all-versions/default/tests/hidlutils_tests.cpp b/audio/common/all-versions/default/tests/hidlutils_tests.cpp
index 40fc5c8..99d2e72 100644
--- a/audio/common/all-versions/default/tests/hidlutils_tests.cpp
+++ b/audio/common/all-versions/default/tests/hidlutils_tests.cpp
@@ -44,8 +44,8 @@
         static_cast<audio_gain_mode_t>(0xFFFFFFFFU);
 // AUDIO_SOURCE_INVALID is framework-only.
 static constexpr audio_source_t kInvalidHalSource = static_cast<audio_source_t>(-1);
-static constexpr audio_stream_type_t kInvalidHalStreamType =
-        static_cast<audio_stream_type_t>(0xFFFFFFFFU);
+// AUDIO_STREAM_DEFAULT is framework-only
+static constexpr audio_stream_type_t kInvalidHalStreamType = static_cast<audio_stream_type_t>(-2);
 static constexpr audio_usage_t kInvalidHalUsage = static_cast<audio_usage_t>(0xFFFFFFFFU);
 
 TEST(HidlUtils, ConvertInvalidChannelMask) {
@@ -660,10 +660,18 @@
     AudioStreamType invalid;
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioStreamTypeFromHal(kInvalidHalStreamType, &invalid));
     audio_stream_type_t halInvalid;
-    EXPECT_EQ(BAD_VALUE, HidlUtils::audioStreamTypeToHal("", &halInvalid));
     EXPECT_EQ(BAD_VALUE, HidlUtils::audioStreamTypeToHal("random string", &halInvalid));
 }
 
+TEST(HidlUtils, ConvertDefaultStreamType) {
+    AudioStreamType streamDefault = "";
+    audio_stream_type_t halStreamDefault;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioStreamTypeToHal(streamDefault, &halStreamDefault));
+    AudioStreamType streamDefaultBack;
+    EXPECT_EQ(NO_ERROR, HidlUtils::audioStreamTypeFromHal(halStreamDefault, &streamDefaultBack));
+    EXPECT_EQ(streamDefault, streamDefaultBack);
+}
+
 TEST(HidlUtils, ConvertStreamType) {
     for (const auto enumVal : xsdc_enum_range<xsd::AudioStreamType>{}) {
         const AudioStreamType streamType = toString(enumVal);