diff --git a/src/nvim/eval/typval.c b/src/nvim/eval/typval.c
index 31e95ef147..d50a5e4bd5 100644
--- a/src/nvim/eval/typval.c
+++ b/src/nvim/eval/typval.c
@@ -2029,7 +2029,9 @@ dictitem_T *tv_dict_item_alloc_len(const char *const key, const size_t key_len)
   FUNC_ATTR_NONNULL_RET FUNC_ATTR_NONNULL_ALL FUNC_ATTR_WARN_UNUSED_RESULT
   FUNC_ATTR_MALLOC
 {
-  dictitem_T *const di = xmalloc(offsetof(dictitem_T, di_key) + key_len + 1);
+  // Allocating a struct smaller than its static size is UB (#37160)
+  dictitem_T *const di = xmalloc(MAX(sizeof(dictitem_T),
+                                     offsetof(dictitem_T, di_key) + key_len + 1));
   memcpy(di->di_key, key, key_len);
   di->di_key[key_len] = NUL;
   di->di_flags = DI_FLAGS_ALLOC;
diff --git a/test/unit/eval/testutil.lua b/test/unit/eval/testutil.lua
index 78788e5837..68669aa145 100644
--- a/test/unit/eval/testutil.lua
+++ b/test/unit/eval/testutil.lua
@@ -413,7 +413,7 @@ local function alloc_len(len, get_ptr)
   if type(len) == 'string' or type(len) == 'table' then
     return #len
   elseif len == nil then
-    return eval.strlen(get_ptr())
+    return tonumber(eval.strlen(get_ptr()))
   else
     return len
   end
@@ -435,7 +435,7 @@ local alloc_logging_t = {
     end)
     return {
       func = 'malloc',
-      args = { ffi.offsetof('dictitem_T', 'di_key') + size + 1 },
+      args = { math.max(ffi.sizeof('dictitem_T'), ffi.offsetof('dictitem_T', 'di_key') + size + 1) },
       ret = void(di),
     }
   end,