diff --git a/lib/isc/jemalloc_shim.h b/lib/isc/jemalloc_shim.h
index ef892f0318..d432917594 100644
--- a/lib/isc/jemalloc_shim.h
+++ b/lib/isc/jemalloc_shim.h
@@ -32,6 +32,66 @@ const char *malloc_conf = NULL;
 #define MALLOCX_ZERO		((int)0x40)
 #define MALLOCX_ZERO_GET(flags) ((bool)(flags & MALLOCX_ZERO))
 
+#if defined(HAVE_MALLOC_SIZE) || defined(HAVE_MALLOC_USABLE_SIZE)
+
+#ifdef HAVE_MALLOC_SIZE
+
+#include <malloc/malloc.h>
+
+static inline size_t
+sallocx(void *ptr, int flags ISC_ATTR_UNUSED) {
+	return malloc_size(ptr);
+}
+
+#elif HAVE_MALLOC_USABLE_SIZE
+
+#ifdef __DragonFly__
+/*
+ * On DragonFly BSD 'man 3 malloc' advises us to include the following
+ * header to have access to malloc_usable_size().
+ */
+#include <malloc_np.h>
+#else
+#include <malloc.h>
+#endif
+
+static inline size_t
+sallocx(void *ptr, int flags ISC_ATTR_UNUSED) {
+	return malloc_usable_size(ptr);
+}
+
+#endif /* HAVE_MALLOC_SIZE */
+
+static inline void *
+mallocx(size_t size, int flags) {
+	void *ptr = malloc(size);
+	INSIST(ptr != NULL);
+
+	if ((flags & MALLOCX_ZERO) != 0) {
+		memset(ptr, 0, size);
+	}
+
+	return ptr;
+}
+
+static inline void
+sdallocx(void *ptr, size_t size ISC_ATTR_UNUSED, int flags ISC_ATTR_UNUSED) {
+	free(ptr);
+}
+
+static inline void *
+rallocx(void *ptr, size_t size, int flags) {
+	REQUIRE(size != 0);
+	REQUIRE((flags & MALLOCX_ZERO) == 0);
+
+	ptr = realloc(ptr, size);
+	INSIST(ptr != NULL);
+
+	return ptr;
+}
+
+#else
+
 typedef union {
 	size_t size;
 	max_align_t __alignment;
@@ -85,4 +145,6 @@ rallocx(void *ptr, size_t size, int flags) {
 	return ptr;
 }
 
+#endif /* defined(HAVE_MALLOC_SIZE) || defined(HAVE_MALLOC_USABLE_SIZE) */
+
 #endif /* !defined(HAVE_JEMALLOC) */
diff --git a/lib/isc/mem.c b/lib/isc/mem.c
index 36498b3e8f..453aa71fba 100644
--- a/lib/isc/mem.c
+++ b/lib/isc/mem.c
@@ -724,7 +724,21 @@ isc__mem_reget(isc_mem_t *ctx, void *old_ptr, size_t old_size, size_t new_size,
 		DELETE_TRACE(ctx, old_ptr, old_size, func, file, line);
 		mem_putstats(ctx, old_size);
 
+		ADJUST_ZERO_ALLOCATION_SIZE(new_size);
+
+#ifdef HAVE_JEMALLOC
 		new_ptr = mem_realloc(ctx, old_ptr, new_size, flags);
+#else
+		new_ptr = mem_realloc(ctx, old_ptr, new_size,
+				      flags & ~ISC__MEM_ZERO);
+
+		if ((flags & ISC__MEM_ZERO) != 0) {
+			if (new_size > old_size) {
+				memset((uint8_t *)new_ptr + old_size, 0,
+				       new_size - old_size);
+			}
+		}
+#endif
 
 		mem_getstats(ctx, new_size);
 		ADD_TRACE(ctx, new_ptr, new_size, func, file, line);
diff --git a/meson.build b/meson.build
index a4af8a153b..4315d697c6 100644
--- a/meson.build
+++ b/meson.build
@@ -718,6 +718,32 @@ if jemalloc_opt.allowed()
     endif
 endif
 
+foreach fn : [
+    'malloc_usable_size',
+]
+    if cc.has_function(
+        fn,
+        prefix: '#include <malloc.h>',
+        args: sys_defines,
+        dependencies: thread_dep,
+    )
+        config.set('HAVE_@0@'.format(fn.to_upper()), 1)
+    endif
+endforeach
+
+foreach fn : [
+    'malloc_size',
+]
+    if cc.has_function(
+        fn,
+        prefix: '#include <malloc/malloc.h>',
+        args: sys_defines,
+        dependencies: thread_dep,
+    )
+        config.set('HAVE_@0@'.format(fn.to_upper()), 1)
+    endif
+endforeach
+
 ## dnstap
 dnstap_dep = null_dep # Will be filled later