diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index 0543a6f4..97b96885 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -755,9 +755,13 @@ static inline uintptr_t _mi_thread_id(void) mi_attr_noexcept {
 // The base version declares the source parameter as MI_SOURCE_XPARAM and can pass it through as MI_SOURCE_XARG
 //
 // The big preprocessor macros that follow emit the 5 declarations with default
-// implementations for the first 4 versions so only the 5th needs to be implemented.
+// implementations for the first 4 versions so only the 5th (base version) needs to be implemented.
+//
+// For example, we write:
+// > MI_ALLOC_API1(inline mi_decl_restrict void*, malloc_small, mi_heap_t*, heap, size_t, size) { ... }
+// to implement `malloc_small` where we can use `MI_SOURCE_XARG` to pass on the possible source argument.
 // -------------------------------------------------------------------------------------------------------------
-#define MI_DEBUG_ONLY(x)  x  // we still allow dbg entry points in release mode to enable linking with a release build
+#define MI_DEBUG_ONLY(x)  x  // we still emit dbg entry points in release mode to enable linking with a release build
 
 #define MI_ALLOC_API1(tp,name,tp0,arg0,tp1,arg1) \
    static tp mi_base_##name(tp0 arg0, tp1 arg1  MI_SOURCE_XPARAM) mi_attr_noexcept; \
@@ -800,6 +804,9 @@ static inline uintptr_t _mi_thread_id(void) mi_attr_noexcept {
    static tp mi_base_##name(tp0 arg0, tp1 arg1, tp2 arg2, tp3 arg3, tp4 arg4, tp5 arg5  MI_SOURCE_XPARAM) mi_attr_noexcept
 
 
+// MI_NEW_API
+// These are for C++ `new` entry points that don't need entries with an explicit heap parameter (and can raise exceptions)
+
 #define MI_NEW_API1(tp,name,tp1,arg1) \
    static tp mi_base_##name(tp1 arg1  MI_SOURCE_XPARAM); \
    tp mi_##name(tp1 arg1) { return mi_base_##name(arg1  MI_SOURCE_XRET()); } \
@@ -818,7 +825,9 @@ static inline uintptr_t _mi_thread_id(void) mi_attr_noexcept {
    MI_DEBUG_ONLY(tp dbg_mi_##name(tp1 arg1, tp2 arg2, tp3 arg3, mi_source_t __mi_source) { (void)__mi_source; return mi_base_##name(arg1, arg2, arg3  MI_SOURCE_XARG); }) \
    static tp mi_base_##name(tp1 arg1, tp2 arg2, tp3 arg3  MI_SOURCE_XPARAM)
 
-
+// MI_SOURCE_API
+// These are for C API entry points that don't need entries with an explicit heap parameter (like `aligned_alloc`)
+// These are marked as noexcept.
 
 #define MI_SOURCE_API1(tp,name,tp1,arg1) \
    static tp mi_base_##name(tp1 arg1  MI_SOURCE_XPARAM); \
diff --git a/include/mimalloc.h b/include/mimalloc.h
index 13c50898..b7a388c2 100644
--- a/include/mimalloc.h
+++ b/include/mimalloc.h
@@ -495,13 +495,13 @@ template<class T1, class T2> bool operator!=(const mi_stl_allocator<T1>&, const
 #else
 #define mi_return_address()     NULL
 #endif
-#define MI_SOURCE_XPARAM        , mi_source_t __mi_source
-#define MI_SOURCE_XARG          , __mi_source
-#define MI_SOURCE_XRET()        , mi_source_ret(mi_return_address())
-#define MI_SOURCE_XLOC()        , mi_source_loc(__FILE__,__LINE__)
-#define MI_SOURCE_ARG(fun,...)  dbg_##fun(__VA_ARGS__  MI_SOURCE_XARG)
-#define MI_SOURCE_RET(fun,...)  dbg_##fun(__VA_ARGS__  MI_SOURCE_XRET())
-#define MI_SOURCE_LOC(fun,...)  dbg_##fun(__VA_ARGS__  MI_SOURCE_XLOC())
+#define MI_SOURCE_XPARAM        , mi_source_t __mi_source                  // declare the extra source parameter
+#define MI_SOURCE_XARG          , __mi_source                              // pass the extra source parameter as a source argument
+#define MI_SOURCE_XRET()        , mi_source_ret(mi_return_address())       // pass the return address as a source argument
+#define MI_SOURCE_XLOC()        , mi_source_loc(__FILE__,__LINE__)         // pass the current source location as a source argument
+#define MI_SOURCE_ARG(fun,...)  dbg_##fun(__VA_ARGS__  MI_SOURCE_XARG)     // call the debug entry with the given source argument
+#define MI_SOURCE_RET(fun,...)  dbg_##fun(__VA_ARGS__  MI_SOURCE_XRET())   // call the debug entry with the return address as the source
+#define MI_SOURCE_LOC(fun,...)  dbg_##fun(__VA_ARGS__  MI_SOURCE_XLOC())   // call the debug entry with the current source location as the source 
 #endif
 
 #if !defined(NDEBUG) && !defined(MI_DEBUG_NO_SOURCE_LOC)
diff --git a/src/alloc.c b/src/alloc.c
index 0498c767..bcd94673 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -11,6 +11,7 @@ terms of the MIT license. A copy of the license can be found in the file
 
 #include <string.h>  // memset, memcpy, strlen
 #include <stdlib.h>  // malloc, exit
+#include <stdio.h>   // snprintf
 #include <wchar.h>   // wcslen
 
 #define MI_IN_ALLOC_C
@@ -240,7 +241,9 @@ static void mi_check_padding(const mi_page_t* page, const mi_block_t* block) {
   size_t size;
   size_t wrong;
   if (!mi_verify_padding(page,block,&size,&wrong)) {
-    _mi_page_block_error_message(EFAULT, page, block, "buffer overflow in heap block (write after %zu bytes)" );
+    char msg[80];
+    snprintf(msg, 79, "buffer overflow in heap block (write after %zu bytes)", (wrong > 0 ? wrong - 1 : wrong));
+    _mi_page_block_error_message(EFAULT, page, block, msg );
   }
 }
 
diff --git a/test/main-override-static.c b/test/main-override-static.c
index fac18ef7..c7c10ddc 100644
--- a/test/main-override-static.c
+++ b/test/main-override-static.c
@@ -17,11 +17,11 @@ int main() {
   mi_version();
 
   // detect double frees and heap corruption
-  // double_free1();
-  // double_free2();
-  // corrupt_free();
-  // block_overflow1();
-  dangling_ptr_write();
+  double_free1();
+  double_free2();
+  corrupt_free();
+  block_overflow1();
+  // dangling_ptr_write();
 
   void* p1 = malloc(78);
   void* p2 = malloc(24);