diff --git a/dlls/dbghelp/stack.c b/dlls/dbghelp/stack.c
index e0180baddf5..3e1ff725470 100644
--- a/dlls/dbghelp/stack.c
+++ b/dlls/dbghelp/stack.c
@@ -95,10 +95,11 @@ static inline void addr_64to32(const ADDRESS64* addr64, ADDRESS* addr32)
 
 BOOL sw_read_mem(struct cpu_stack_walk* csw, DWORD64 addr, void* ptr, DWORD sz)
 {
+    DWORD bytes_read = 0;
     if (csw->is32)
-        return csw->u.s32.f_read_mem(csw->hProcess, addr, ptr, sz, NULL);
+        return csw->u.s32.f_read_mem(csw->hProcess, addr, ptr, sz, &bytes_read);
     else
-        return csw->u.s64.f_read_mem(csw->hProcess, addr, ptr, sz, NULL);
+        return csw->u.s64.f_read_mem(csw->hProcess, addr, ptr, sz, &bytes_read);
 }
 
 DWORD64 sw_xlat_addr(struct cpu_stack_walk* csw, ADDRESS64* addr)