diff --git a/src/input/TextInputStream.cxx b/src/input/TextInputStream.cxx
index 25b9b42fe..d7cb440b3 100644
--- a/src/input/TextInputStream.cxx
+++ b/src/input/TextInputStream.cxx
@@ -63,7 +63,7 @@ bool TextInputStream::ReadLine(std::string &line)
 			   the current line */
 			dest = buffer.Write();
 			assert(!dest.IsEmpty());
-			dest.data[0] = '\n';
+			dest[0] = '\n';
 			buffer.Append(1);
 		}
 	} while (p == nullptr);
diff --git a/src/pcm/FallbackResampler.cxx b/src/pcm/FallbackResampler.cxx
index d005a831c..bd3f20d86 100644
--- a/src/pcm/FallbackResampler.cxx
+++ b/src/pcm/FallbackResampler.cxx
@@ -85,7 +85,7 @@ pcm_resample_fallback(PcmBuffer &buffer,
 		while (dest_pos < dest_samples) {
 			unsigned src_pos = dest_pos * src_rate / dest_rate;
 
-			dest_buffer[dest_pos++] = src.data[src_pos];
+			dest_buffer[dest_pos++] = src[src_pos];
 		}
 		break;
 	case 2:
@@ -93,8 +93,8 @@ pcm_resample_fallback(PcmBuffer &buffer,
 			unsigned src_pos = dest_pos * src_rate / dest_rate;
 			src_pos &= ~1;
 
-			dest_buffer[dest_pos++] = src.data[src_pos];
-			dest_buffer[dest_pos++] = src.data[src_pos + 1];
+			dest_buffer[dest_pos++] = src[src_pos];
+			dest_buffer[dest_pos++] = src[src_pos + 1];
 		}
 		break;
 	}
diff --git a/src/util/ConstBuffer.hxx b/src/util/ConstBuffer.hxx
index 7f1fa5aa6..6754cb065 100644
--- a/src/util/ConstBuffer.hxx
+++ b/src/util/ConstBuffer.hxx
@@ -143,6 +143,17 @@ struct ConstBuffer {
 	constexpr const_iterator cend() const {
 		return data + size;
 	}
+
+#ifdef NDEBUG
+	constexpr
+#endif
+	const T &operator[](size_type i) const {
+#ifndef NDEBUG
+		assert(i < size);
+#endif
+
+		return data[i];
+	}
 };
 
 #endif
diff --git a/src/util/WritableBuffer.hxx b/src/util/WritableBuffer.hxx
index 64e6d0c62..d13f80867 100644
--- a/src/util/WritableBuffer.hxx
+++ b/src/util/WritableBuffer.hxx
@@ -145,6 +145,17 @@ struct WritableBuffer {
 	constexpr const_iterator cend() const {
 		return data + size;
 	}
+
+#ifdef NDEBUG
+	constexpr
+#endif
+	T &operator[](size_type i) const {
+#ifndef NDEBUG
+		assert(i < size);
+#endif
+
+		return data[i];
+	}
 };
 
 #endif
diff --git a/test/test_pcm_channels.cxx b/test/test_pcm_channels.cxx
index 85ad0c248..a36fb39f3 100644
--- a/test/test_pcm_channels.cxx
+++ b/test/test_pcm_channels.cxx
@@ -39,7 +39,7 @@ PcmChannelsTest::TestChannels16()
 	CPPUNIT_ASSERT_EQUAL(N, dest.size);
 	for (unsigned i = 0; i < N; ++i)
 		CPPUNIT_ASSERT_EQUAL(int16_t((src[i * 2] + src[i * 2 + 1]) / 2),
-				     dest.data[i]);
+				     dest[i]);
 
 	/* mono to stereo */
 
@@ -47,8 +47,8 @@ PcmChannelsTest::TestChannels16()
 	CPPUNIT_ASSERT(!dest.IsNull());
 	CPPUNIT_ASSERT_EQUAL(N * 4, dest.size);
 	for (unsigned i = 0; i < N; ++i) {
-		CPPUNIT_ASSERT_EQUAL(src[i], dest.data[i * 2]);
-		CPPUNIT_ASSERT_EQUAL(src[i], dest.data[i * 2 + 1]);
+		CPPUNIT_ASSERT_EQUAL(src[i], dest[i * 2]);
+		CPPUNIT_ASSERT_EQUAL(src[i], dest[i * 2 + 1]);
 	}
 }
 
@@ -67,7 +67,7 @@ PcmChannelsTest::TestChannels32()
 	CPPUNIT_ASSERT_EQUAL(N, dest.size);
 	for (unsigned i = 0; i < N; ++i)
 		CPPUNIT_ASSERT_EQUAL(int32_t(((int64_t)src[i * 2] + (int64_t)src[i * 2 + 1]) / 2),
-				     dest.data[i]);
+				     dest[i]);
 
 	/* mono to stereo */
 
@@ -75,7 +75,7 @@ PcmChannelsTest::TestChannels32()
 	CPPUNIT_ASSERT(!dest.IsNull());
 	CPPUNIT_ASSERT_EQUAL(N * 4, dest.size);
 	for (unsigned i = 0; i < N; ++i) {
-		CPPUNIT_ASSERT_EQUAL(src[i], dest.data[i * 2]);
-		CPPUNIT_ASSERT_EQUAL(src[i], dest.data[i * 2 + 1]);
+		CPPUNIT_ASSERT_EQUAL(src[i], dest[i * 2]);
+		CPPUNIT_ASSERT_EQUAL(src[i], dest[i * 2 + 1]);
 	}
 }
diff --git a/test/test_pcm_format.cxx b/test/test_pcm_format.cxx
index 6393d484b..94c55ab16 100644
--- a/test/test_pcm_format.cxx
+++ b/test/test_pcm_format.cxx
@@ -39,7 +39,7 @@ PcmFormatTest::TestFormat8to16()
 	CPPUNIT_ASSERT_EQUAL(N, d.size);
 
 	for (size_t i = 0; i < N; ++i)
-		CPPUNIT_ASSERT_EQUAL(int(src[i]), d.data[i] >> 8);
+		CPPUNIT_ASSERT_EQUAL(int(src[i]), d[i] >> 8);
 }
 
 void
@@ -54,7 +54,7 @@ PcmFormatTest::TestFormat16to24()
 	CPPUNIT_ASSERT_EQUAL(N, d.size);
 
 	for (size_t i = 0; i < N; ++i)
-		CPPUNIT_ASSERT_EQUAL(int(src[i]), d.data[i] >> 8);
+		CPPUNIT_ASSERT_EQUAL(int(src[i]), d[i] >> 8);
 }
 
 void
@@ -69,7 +69,7 @@ PcmFormatTest::TestFormat16to32()
 	CPPUNIT_ASSERT_EQUAL(N, d.size);
 
 	for (size_t i = 0; i < N; ++i)
-		CPPUNIT_ASSERT_EQUAL(int(src[i]), d.data[i] >> 16);
+		CPPUNIT_ASSERT_EQUAL(int(src[i]), d[i] >> 16);
 }
 
 void
@@ -84,8 +84,8 @@ PcmFormatTest::TestFormatFloat()
 	CPPUNIT_ASSERT_EQUAL(N, f.size);
 
 	for (size_t i = 0; i != f.size; ++i) {
-		CPPUNIT_ASSERT(f.data[i] >= -1.);
-		CPPUNIT_ASSERT(f.data[i] <= 1.);
+		CPPUNIT_ASSERT(f[i] >= -1.);
+		CPPUNIT_ASSERT(f[i] <= 1.);
 	}
 
 	PcmDither dither;
@@ -96,5 +96,5 @@ PcmFormatTest::TestFormatFloat()
 	CPPUNIT_ASSERT_EQUAL(N, d.size);
 
 	for (size_t i = 0; i < N; ++i)
-		CPPUNIT_ASSERT_EQUAL(src[i], d.data[i]);
+		CPPUNIT_ASSERT_EQUAL(src[i], d[i]);
 }
diff --git a/test/test_pcm_volume.cxx b/test/test_pcm_volume.cxx
index d08c7efb0..de880563d 100644
--- a/test/test_pcm_volume.cxx
+++ b/test/test_pcm_volume.cxx
@@ -61,8 +61,8 @@ TestVolume(G g=G())
 	const auto _dest = ConstBuffer<value_type>::FromVoid(dest);
 	for (unsigned i = 0; i < N; ++i) {
 		const auto expected = (_src[i] + 1) / 2;
-		CPPUNIT_ASSERT(_dest.data[i] >= expected - 4);
-		CPPUNIT_ASSERT(_dest.data[i] <= expected + 4);
+		CPPUNIT_ASSERT(_dest[i] >= expected - 4);
+		CPPUNIT_ASSERT(_dest[i] <= expected + 4);
 	}
 
 	pv.Close();
@@ -119,7 +119,7 @@ PcmVolumeTest::TestVolumeFloat()
 
 	const auto _dest = ConstBuffer<float>::FromVoid(dest);
 	for (unsigned i = 0; i < N; ++i)
-		CPPUNIT_ASSERT_DOUBLES_EQUAL(_src[i] / 2, _dest.data[i], 1);
+		CPPUNIT_ASSERT_DOUBLES_EQUAL(_src[i] / 2, _dest[i], 1);
 
 	pv.Close();
 }