diff --git a/src/pcm_convert.c b/src/pcm_convert.c
index 4dbeee41f..c145e437a 100644
--- a/src/pcm_convert.c
+++ b/src/pcm_convert.c
@@ -200,7 +200,8 @@ pcm_convert_24_packed(struct pcm_convert_state *state,
 	size_t dest_size = num_samples * 3;
 
 	uint8_t *dest = pcm_buffer_get(&state->pack_buffer, dest_size);
-	pcm_pack_24(dest, buffer, num_samples, dest_format->reverse_endian);
+	pcm_pack_24(dest, buffer, buffer + num_samples,
+		    dest_format->reverse_endian);
 
 	*dest_size_r = dest_size;
 	return dest;
diff --git a/src/pcm_format.c b/src/pcm_format.c
index 544b0ccd9..21459f0f4 100644
--- a/src/pcm_format.c
+++ b/src/pcm_format.c
@@ -54,7 +54,7 @@ pcm_convert_24_to_24p32(struct pcm_buffer *buffer, const uint8_t *src,
 			unsigned num_samples)
 {
 	int32_t *dest = pcm_buffer_get(buffer, num_samples * 4);
-	pcm_unpack_24(dest, src, num_samples, false);
+	pcm_unpack_24(dest, src, src + num_samples * 3, false);
 	return dest;
 }
 
diff --git a/src/pcm_pack.c b/src/pcm_pack.c
index 680d2a32f..94fda5910 100644
--- a/src/pcm_pack.c
+++ b/src/pcm_pack.c
@@ -35,19 +35,19 @@ pack_sample(uint8_t *dest, const int32_t *src0, bool reverse_endian)
 }
 
 void
-pcm_pack_24(uint8_t *dest, const int32_t *src, unsigned num_samples,
+pcm_pack_24(uint8_t *dest, const int32_t *src, const int32_t *src_end,
 	    bool reverse_endian)
 {
 	/* duplicate loop to help the compiler's optimizer (constant
 	   parameter to the pack_sample() inline function) */
 
 	if (G_LIKELY(!reverse_endian)) {
-		while (num_samples-- > 0) {
+		while (src < src_end) {
 			pack_sample(dest, src++, false);
 			dest += 3;
 		}
 	} else {
-		while (num_samples-- > 0) {
+		while (src < src_end) {
 			pack_sample(dest, src++, true);
 			dest += 3;
 		}
@@ -73,19 +73,19 @@ unpack_sample(int32_t *dest0, const uint8_t *src, bool reverse_endian)
 }
 
 void
-pcm_unpack_24(int32_t *dest, const uint8_t *src, unsigned num_samples,
+pcm_unpack_24(int32_t *dest, const uint8_t *src, const uint8_t *src_end,
 	      bool reverse_endian)
 {
 	/* duplicate loop to help the compiler's optimizer (constant
 	   parameter to the unpack_sample() inline function) */
 
 	if (G_LIKELY(!reverse_endian)) {
-		while (num_samples-- > 0) {
+		while (src < src_end) {
 			unpack_sample(dest++, src, false);
 			src += 3;
 		}
 	} else {
-		while (num_samples-- > 0) {
+		while (src < src_end) {
 			unpack_sample(dest++, src, true);
 			src += 3;
 		}
diff --git a/src/pcm_pack.h b/src/pcm_pack.h
index 0055e91df..6f275608c 100644
--- a/src/pcm_pack.h
+++ b/src/pcm_pack.h
@@ -40,7 +40,7 @@
  * @param reverse_endian is src and dest in non-host byte order?
  */
 void
-pcm_pack_24(uint8_t *dest, const int32_t *src, unsigned num_samples,
+pcm_pack_24(uint8_t *dest, const int32_t *src, const int32_t *src_end,
 	    bool reverse_endian);
 
 /**
@@ -53,7 +53,7 @@ pcm_pack_24(uint8_t *dest, const int32_t *src, unsigned num_samples,
  * @param reverse_endian is src and dest in non-host byte order?
  */
 void
-pcm_unpack_24(int32_t *dest, const uint8_t *src, unsigned num_samples,
+pcm_unpack_24(int32_t *dest, const uint8_t *src, const uint8_t *src_end,
 	      bool reverse_endian);
 
 #endif
diff --git a/test/test_pcm_pack.c b/test/test_pcm_pack.c
index 81bc32575..921bb7932 100644
--- a/test/test_pcm_pack.c
+++ b/test/test_pcm_pack.c
@@ -44,7 +44,7 @@ test_pcm_pack_24(void)
 
 	uint8_t dest[N * 3];
 
-	pcm_pack_24(dest, src, N, false);
+	pcm_pack_24(dest, src, src + N, false);
 
 	for (unsigned i = 0; i < N; ++i) {
 		int32_t d;
@@ -71,7 +71,7 @@ test_pcm_unpack_24(void)
 
 	int32_t dest[N];
 
-	pcm_unpack_24(dest, src, N, false);
+	pcm_unpack_24(dest, src, src + G_N_ELEMENTS(src), false);
 
 	for (unsigned i = 0; i < N; ++i) {
 		int32_t s;