diff --git a/core/os/os_darwin.odin b/core/os/os_darwin.odin
index d40c80aeb..6fa43bf09 100644
--- a/core/os/os_darwin.odin
+++ b/core/os/os_darwin.odin
@@ -530,6 +530,8 @@ heap_alloc :: proc(size: int) -> rawptr {
 	return _unix_calloc(1, size)
 }
 heap_resize :: proc(ptr: rawptr, new_size: int) -> rawptr {
+	// NOTE: _unix_realloc doesn't guarantee new memory will be zeroed on
+	// POSIX platforms. Ensure your caller takes this into account.
 	return _unix_realloc(ptr, new_size)
 }
 heap_free :: proc(ptr: rawptr) {
diff --git a/core/os/os_freebsd.odin b/core/os/os_freebsd.odin
index e9314b468..82317532d 100644
--- a/core/os/os_freebsd.odin
+++ b/core/os/os_freebsd.odin
@@ -378,6 +378,8 @@ heap_alloc :: proc(size: int) -> rawptr {
 }
 
 heap_resize :: proc(ptr: rawptr, new_size: int) -> rawptr {
+	// NOTE: _unix_realloc doesn't guarantee new memory will be zeroed on
+	// POSIX platforms. Ensure your caller takes this into account.
 	return _unix_realloc(ptr, c.size_t(new_size));
 }
 
diff --git a/core/os/os_linux.odin b/core/os/os_linux.odin
index 260a051ce..116fbdba5 100644
--- a/core/os/os_linux.odin
+++ b/core/os/os_linux.odin
@@ -543,6 +543,8 @@ heap_alloc :: proc(size: int) -> rawptr {
 }
 
 heap_resize :: proc(ptr: rawptr, new_size: int) -> rawptr {
+	// NOTE: _unix_realloc doesn't guarantee new memory will be zeroed on
+	// POSIX platforms. Ensure your caller takes this into account.
 	return _unix_realloc(ptr, c.size_t(new_size))
 }