diff --git a/dlmalloc-rs b/dlmalloc-rs
index e4ba849349..3b0ee3b467 160000
--- a/dlmalloc-rs
+++ b/dlmalloc-rs
@@ -1 +1 @@
-Subproject commit e4ba8493497c72e15f2b9d428e1dea17e26bf188
+Subproject commit 3b0ee3b467401229b005df226bd32990ee7e3414
diff --git a/src/header/malloc/mod.rs b/src/header/malloc/mod.rs
index 5061e2098d..54977f414b 100644
--- a/src/header/malloc/mod.rs
+++ b/src/header/malloc/mod.rs
@@ -40,3 +40,9 @@ pub unsafe extern "C" fn pvalloc(size: size_t) -> *mut c_void {
         }
     }
 }
+
+/// See <https://man7.org/linux/man-pages/man3/malloc_usable_size.3.html>.
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn malloc_usable_size(ptr: *mut c_void) -> size_t {
+    platform::alloc_usable_size(ptr)
+}
diff --git a/src/platform/allocator/mod.rs b/src/platform/allocator/mod.rs
index 61c49120e4..7dddfb8adc 100644
--- a/src/platform/allocator/mod.rs
+++ b/src/platform/allocator/mod.rs
@@ -97,3 +97,10 @@ pub unsafe fn free(ptr: *mut c_void) {
     }
     (*ALLOCATOR.get()).lock().free(ptr.cast())
 }
+
+pub unsafe fn alloc_usable_size(ptr: *mut c_void) -> size_t {
+    if ptr.is_null() {
+        return 0;
+    }
+    (*ALLOCATOR.get()).lock().usable_size(ptr.cast())
+}
diff --git a/tests/Makefile b/tests/Makefile
index 0f3489d4a8..b8d479c99c 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -49,6 +49,7 @@ EXPECT_NAMES=\
 	locale/duplocale \
 	locale/newlocale \
 	locale/setlocale \
+	malloc/usable_size \
 	math \
 	regex \
 	select \
diff --git a/tests/expected/bins_dynamic/malloc/usable_size.stderr b/tests/expected/bins_dynamic/malloc/usable_size.stderr
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/expected/bins_dynamic/malloc/usable_size.stdout b/tests/expected/bins_dynamic/malloc/usable_size.stdout
new file mode 100644
index 0000000000..4188b67b66
--- /dev/null
+++ b/tests/expected/bins_dynamic/malloc/usable_size.stdout
@@ -0,0 +1,2 @@
+malloc: 27 bytes
+malloc_usable_size: 48 bytes
diff --git a/tests/expected/bins_static/malloc/usable_size.stderr b/tests/expected/bins_static/malloc/usable_size.stderr
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/expected/bins_static/malloc/usable_size.stdout b/tests/expected/bins_static/malloc/usable_size.stdout
new file mode 100644
index 0000000000..4188b67b66
--- /dev/null
+++ b/tests/expected/bins_static/malloc/usable_size.stdout
@@ -0,0 +1,2 @@
+malloc: 27 bytes
+malloc_usable_size: 48 bytes
diff --git a/tests/malloc/usable_size.c b/tests/malloc/usable_size.c
new file mode 100644
index 0000000000..933ebf03f2
--- /dev/null
+++ b/tests/malloc/usable_size.c
@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <malloc.h>
+#include <string.h>
+#include <assert.h>
+
+int main(void) {
+    size_t request_size = 27;
+    char *ptr = (char *)malloc(request_size);
+
+    if (!ptr) {
+        fprintf(stderr, "Allocation failed\n");
+        return 1;
+    }
+
+    size_t actual_size = malloc_usable_size(ptr);
+
+    printf("malloc: %zu bytes\n", request_size);
+    printf("malloc_usable_size: %zu bytes\n", actual_size);
+
+    assert(actual_size >= request_size);
+    memset(ptr, 'A', actual_size); 
+    ptr[actual_size - 1] = '\0';
+
+    assert(ptr[0] == 'A');
+    assert(ptr[actual_size - 2] == 'A');
+    assert(ptr[actual_size - 1] == '\0');
+    free(ptr);
+
+    return 0;
+}