diff --git a/include/jemalloc/internal/arena_inlines_b.h b/include/jemalloc/internal/arena_inlines_b.h
index 5df8e858..5410b160 100644
--- a/include/jemalloc/internal/arena_inlines_b.h
+++ b/include/jemalloc/internal/arena_inlines_b.h
@@ -228,9 +228,10 @@ large_dalloc_safety_checks(edata_t *edata, void *ptr, szind_t szind) {
 		    (uintptr_t)edata_addr_get(edata));
 		return true;
 	}
-	if (unlikely(sz_index2size(szind) != edata_usize_get(edata))) {
-		safety_check_fail_sized_dealloc(/* current_dealloc */ true,
-		    ptr);
+	size_t input_size = sz_index2size(szind);
+	if (unlikely(input_size != edata_usize_get(edata))) {
+		safety_check_fail_sized_dealloc(/* current_dealloc */ true, ptr,
+		    /* true_size */ edata_usize_get(edata), input_size);
 		return true;
 	}
 
diff --git a/include/jemalloc/internal/safety_check.h b/include/jemalloc/internal/safety_check.h
index b27ac088..f10c68e4 100644
--- a/include/jemalloc/internal/safety_check.h
+++ b/include/jemalloc/internal/safety_check.h
@@ -1,7 +1,8 @@
 #ifndef JEMALLOC_INTERNAL_SAFETY_CHECK_H
 #define JEMALLOC_INTERNAL_SAFETY_CHECK_H
 
-void safety_check_fail_sized_dealloc(bool current_dealloc, const void *ptr);
+void safety_check_fail_sized_dealloc(bool current_dealloc, const void *ptr,
+    size_t true_size, size_t input_size);
 void safety_check_fail(const char *format, ...);
 /* Can set to NULL for a default. */
 void safety_check_set_abort(void (*abort_fn)(const char *));
diff --git a/src/jemalloc.c b/src/jemalloc.c
index 9d038806..3bccac95 100644
--- a/src/jemalloc.c
+++ b/src/jemalloc.c
@@ -2751,7 +2751,9 @@ maybe_check_alloc_ctx(tsd_t *tsd, void *ptr, emap_alloc_ctx_t *alloc_ctx) {
 		    &dbg_ctx);
 		if (alloc_ctx->szind != dbg_ctx.szind) {
 			safety_check_fail_sized_dealloc(
-			    /* current_dealloc */ true, ptr);
+			    /* current_dealloc */ true, ptr,
+			    /* true_size */ sz_size2index(dbg_ctx.szind),
+			    /* input_size */ sz_size2index(alloc_ctx->szind));
 			return true;
 		}
 		if (alloc_ctx->slab != dbg_ctx.slab) {
@@ -2800,9 +2802,13 @@ isfree(tsd_t *tsd, void *ptr, size_t usize, tcache_t *tcache, bool slow_path) {
 
 			if (config_opt_safety_checks) {
 				/* Small alloc may have !slab (sampled). */
-				if (alloc_ctx.szind != sz_size2index(usize)) {
-					safety_check_fail_sized_dealloc(true,
-					    ptr);
+				if (unlikely(alloc_ctx.szind !=
+				    sz_size2index(usize))) {
+					safety_check_fail_sized_dealloc(
+					    /* current_dealloc */ true, ptr,
+					    /* true_size */ sz_index2size(
+					    alloc_ctx.szind),
+					    /* input_size */ usize);
 				}
 			}
 		} else {
diff --git a/src/safety_check.c b/src/safety_check.c
index 0dff9348..9747afef 100644
--- a/src/safety_check.c
+++ b/src/safety_check.c
@@ -3,14 +3,16 @@
 
 static void (*safety_check_abort)(const char *message);
 
-void safety_check_fail_sized_dealloc(bool current_dealloc, const void *ptr) {
+void safety_check_fail_sized_dealloc(bool current_dealloc, const void *ptr,
+    size_t true_size, size_t input_size) {
 	char *src = current_dealloc ? "the current pointer being freed" :
 	    "in thread cache, possibly from previous deallocations";
 
-	safety_check_fail("<jemalloc>: size mismatch detected, likely caused by"
-	    " application sized deallocation bugs (source address: %p, %s). "
-	    "Suggest building with --enable-debug or address sanitizer for "
-	    "debugging. Abort.\n", ptr, src);
+	safety_check_fail("<jemalloc>: size mismatch detected (true size %zu "
+	    "vs input size %zu), likely caused by application sized "
+	    "dealloction bugs (source address: %p, %s). Suggest building with "
+	    "--enable-debug or address sanitizer for debugging. Abort.\n",
+	    true_size, input_size, ptr, src);
 }
 
 void safety_check_set_abort(void (*abort_fn)(const char *)) {
diff --git a/src/tcache.c b/src/tcache.c
index 3489e724..39a4ea6e 100644
--- a/src/tcache.c
+++ b/src/tcache.c
@@ -255,10 +255,14 @@ tcache_bin_flush_size_check_fail(cache_bin_ptr_array_t *arr, szind_t szind,
     size_t nptrs, emap_batch_lookup_result_t *edatas) {
 	bool found_mismatch = false;
 	for (size_t i = 0; i < nptrs; i++) {
-		if (edata_szind_get(edatas[i].edata) != szind) {
+		szind_t true_szind = edata_szind_get(edatas[i].edata);
+		if (true_szind != szind) {
 			found_mismatch = true;
-			safety_check_fail_sized_dealloc(false,
-			    tcache_bin_flush_ptr_getter(arr, i));
+			safety_check_fail_sized_dealloc(
+			    /* current_dealloc */ false,
+			    /* ptr */ tcache_bin_flush_ptr_getter(arr, i),
+			    /* true_size */ sz_index2size(true_szind),
+			    /* input_size */ sz_index2size(szind));
 		}
 	}
 	assert(found_mismatch);