diff --git a/CHANGELOG b/CHANGELOG
index dac0ea5a..95b8d9cf 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -19,6 +19,10 @@ HISTORY
 
   ++ New features:
 
+  2009-04-25 Simon Goldschmidt
+  * mem.c, opt.h: Added option MEM_USE_POOLS_TRY_BIGGER_POOL to try the next
+    bigger malloc pool if one is empty (only usable with MEM_USE_POOLS).
+
   2009-04-21 Simon Goldschmidt
   * dns.c, init.c, dns.h, opt.h: task #7507, patch #6786: DNS supports static
     hosts table. New configuration options DNS_LOCAL_HOSTLIST and
@@ -88,6 +92,11 @@ HISTORY
 
   ++ Bugfixes:
 
+  2009-04-25 Simon Goldschmidt
+  * memp.c, mem.c, memp.h, mem_std.h: bug #26213 "Problem with memory allocation
+    when debugging": memp_sizes contained the wrong sizes (including sanity
+    regions); memp pools for MEM_USE_POOLS were too small
+
   2009-04-24 Simon Goldschmidt, Frédéric Bernon
   * inet.c: patch #6765: Fix a small problem with the last changes (incorrect
     behavior, with with ip address string not ended by a '\0', a space or a
diff --git a/src/core/mem.c b/src/core/mem.c
index 2ee5cfc7..b5f13ab3 100644
--- a/src/core/mem.c
+++ b/src/core/mem.c
@@ -67,14 +67,6 @@
 #if MEM_USE_POOLS
 /* lwIP head implemented with different sized pools */
 
-/**
- * This structure is used to save the pool one element came from.
- */
-struct mem_helper
-{
-   memp_t poolnr;
-};
-
 /**
  * Allocate memory: determine the smallest pool that is big enough
  * to contain an element of 'size' and get an element from that pool.
@@ -85,13 +77,17 @@ struct mem_helper
 void *
 mem_malloc(mem_size_t size)
 {
-  struct mem_helper *element;
+  struct memp_malloc_helper *element;
   memp_t poolnr;
+  mem_size_t required_size = size + sizeof(struct memp_malloc_helper);
 
   for (poolnr = MEMP_POOL_FIRST; poolnr <= MEMP_POOL_LAST; poolnr++) {
+#if MEM_USE_POOLS_TRY_BIGGER_POOL
+again:
+#endif /* MEM_USE_POOLS_TRY_BIGGER_POOL */
     /* is this pool big enough to hold an element of the required size
-       plus a struct mem_helper that saves the pool this element came from? */
-    if ((size + sizeof(struct mem_helper)) <= memp_sizes[poolnr]) {
+       plus a struct memp_malloc_helper that saves the pool this element came from? */
+    if (required_size <= memp_sizes[poolnr]) {
       break;
     }
   }
@@ -99,17 +95,23 @@ mem_malloc(mem_size_t size)
     LWIP_ASSERT("mem_malloc(): no pool is that big!", 0);
     return NULL;
   }
-  element = (struct mem_helper*)memp_malloc(poolnr);
+  element = (struct memp_malloc_helper*)memp_malloc(poolnr);
   if (element == NULL) {
     /* No need to DEBUGF or ASSERT: This error is already
        taken care of in memp.c */
-    /** @todo: we could try a bigger pool if this one is empty! */
+#if MEM_USE_POOLS_TRY_BIGGER_POOL
+    /** Try a bigger pool if this one is empty! */
+    if (poolnr < MEMP_POOL_LAST) {
+      poolnr++;
+      goto again;
+    }
+#endif /* MEM_USE_POOLS_TRY_BIGGER_POOL */
     return NULL;
   }
 
   /* save the pool number this element came from */
   element->poolnr = poolnr;
-  /* and return a pointer to the memory directly after the struct mem_helper */
+  /* and return a pointer to the memory directly after the struct memp_malloc_helper */
   element++;
 
   return element;
@@ -125,12 +127,12 @@ mem_malloc(mem_size_t size)
 void
 mem_free(void *rmem)
 {
-  struct mem_helper *hmem = (struct mem_helper*)rmem;
+  struct memp_malloc_helper *hmem = (struct memp_malloc_helper*)rmem;
 
   LWIP_ASSERT("rmem != NULL", (rmem != NULL));
   LWIP_ASSERT("rmem == MEM_ALIGN(rmem)", (rmem == LWIP_MEM_ALIGN(rmem)));
 
-  /* get the original struct mem_helper */
+  /* get the original struct memp_malloc_helper */
   hmem--;
 
   LWIP_ASSERT("hmem != NULL", (hmem != NULL));
diff --git a/src/core/memp.c b/src/core/memp.c
index 01793ab5..dfc32213 100644
--- a/src/core/memp.c
+++ b/src/core/memp.c
@@ -122,7 +122,7 @@ static struct memp *memp_tab[MEMP_MAX];
 static
 #endif
 const u16_t memp_sizes[MEMP_MAX] = {
-#define LWIP_MEMPOOL(name,num,size,desc)  MEMP_ALIGN_SIZE(size),
+#define LWIP_MEMPOOL(name,num,size,desc)  LWIP_MEM_ALIGN_SIZE(size),
 #include "lwip/memp_std.h"
 };
 
@@ -193,7 +193,7 @@ memp_overflow_check_element(struct memp *p, u16_t memp_size)
   }
 #endif
 #if MEMP_SANITY_REGION_AFTER_ALIGNED > 0
-  m = (u8_t*)p + MEMP_SIZE + memp_size - MEMP_SANITY_REGION_AFTER_ALIGNED;
+  m = (u8_t*)p + MEMP_SIZE + memp_size;
   for (k = 0; k < MEMP_SANITY_REGION_AFTER_ALIGNED; k++) {
     if (m[k] != 0xcd) {
       LWIP_ASSERT("detected memp overflow!", 0);
@@ -218,7 +218,7 @@ memp_overflow_check_all(void)
     p = p;
     for (j = 0; j < memp_num[i]; ++j) {
       memp_overflow_check_element(p, memp_sizes[i]);
-      p = (struct memp*)((u8_t*)p + MEMP_SIZE + memp_sizes[i]);
+      p = (struct memp*)((u8_t*)p + MEMP_SIZE + memp_sizes[i] + MEMP_SANITY_REGION_AFTER_ALIGNED);
     }
   }
 }
@@ -242,10 +242,10 @@ memp_overflow_init(void)
       memset(m, 0xcd, MEMP_SANITY_REGION_BEFORE_ALIGNED);
 #endif
 #if MEMP_SANITY_REGION_AFTER_ALIGNED > 0
-      m = (u8_t*)p + MEMP_SIZE + memp_sizes[i] - MEMP_SANITY_REGION_AFTER_ALIGNED;
+      m = (u8_t*)p + MEMP_SIZE + memp_sizes[i];
       memset(m, 0xcd, MEMP_SANITY_REGION_AFTER_ALIGNED);
 #endif
-      p = (struct memp*)((u8_t*)p + MEMP_SIZE + memp_sizes[i]);
+      p = (struct memp*)((u8_t*)p + MEMP_SIZE + memp_sizes[i] + MEMP_SANITY_REGION_AFTER_ALIGNED);
     }
   }
 }
@@ -277,7 +277,11 @@ memp_init(void)
     for (j = 0; j < memp_num[i]; ++j) {
       memp->next = memp_tab[i];
       memp_tab[i] = memp;
-      memp = (struct memp *)((u8_t *)memp + MEMP_SIZE + memp_sizes[i]);
+      memp = (struct memp *)((u8_t *)memp + MEMP_SIZE + memp_sizes[i]
+#if MEMP_OVERFLOW_CHECK
+        + MEMP_SANITY_REGION_AFTER_ALIGNED
+#endif
+      );
     }
   }
 #if MEMP_OVERFLOW_CHECK
@@ -317,8 +321,8 @@ memp_malloc_fn(memp_t type, const char* file, const int line)
 
   memp = memp_tab[type];
   
-  if (memp != NULL) {    
-    memp_tab[type] = memp->next;    
+  if (memp != NULL) {
+    memp_tab[type] = memp->next;
 #if MEMP_OVERFLOW_CHECK
     memp->next = NULL;
     memp->file = file;
diff --git a/src/include/lwip/memp.h b/src/include/lwip/memp.h
index 45b1f39b..f0d07399 100644
--- a/src/include/lwip/memp.h
+++ b/src/include/lwip/memp.h
@@ -89,6 +89,14 @@ extern const u16_t memp_sizes[MEMP_MAX];
 
 #else /* MEMP_MEM_MALLOC */
 
+#if MEM_USE_POOLS
+/** This structure is used to save the pool one element came from. */
+struct memp_malloc_helper
+{
+   memp_t poolnr;
+};
+#endif /* MEM_USE_POOLS */
+
 void  memp_init(void);
 
 #if MEMP_OVERFLOW_CHECK
diff --git a/src/include/lwip/memp_std.h b/src/include/lwip/memp_std.h
index c314bf87..34469032 100644
--- a/src/include/lwip/memp_std.h
+++ b/src/include/lwip/memp_std.h
@@ -10,8 +10,9 @@
  * above, then will declare #2 & #3 to be just standard mempools.
  */
 #ifndef LWIP_MALLOC_MEMPOOL
-/* This treats "malloc pools" just like any other pool */
-#define LWIP_MALLOC_MEMPOOL(num, size) LWIP_MEMPOOL(POOL_##size, num, size, "MALLOC_"#size)
+/* This treats "malloc pools" just like any other pool.
+   The pools are a little bigger to provide 'size' as the amount of user data. */
+#define LWIP_MALLOC_MEMPOOL(num, size) LWIP_MEMPOOL(POOL_##size, num, (size + sizeof(struct memp_malloc_helper)), "MALLOC_"#size)
 #define LWIP_MALLOC_MEMPOOL_START
 #define LWIP_MALLOC_MEMPOOL_END
 #endif /* LWIP_MALLOC_MEMPOOL */ 
diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 984d0235..ebb3c9ab 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -149,11 +149,20 @@
  * MEM_USE_POOLS==1: Use an alternative to malloc() by allocating from a set
  * of memory pools of various sizes. When mem_malloc is called, an element of
  * the smallest pool that can provide the length needed is returned.
+ * To use this, MEMP_USE_CUSTOM_POOLS also has to be enabled.
  */
 #ifndef MEM_USE_POOLS
 #define MEM_USE_POOLS                   0
 #endif
 
+/**
+ * MEM_USE_POOLS_TRY_BIGGER_POOL==1: if one malloc-pool is empty, try the next
+ * bigger pool - WARNING: THIS MIGHT WASTE MEMORY but it can make a system more
+ * reliable. */
+#ifndef MEM_USE_POOLS_TRY_BIGGER_POOL
+#define MEM_USE_POOLS_TRY_BIGGER_POOL   0
+#endif
+
 /**
  * MEMP_USE_CUSTOM_POOLS==1: whether to include a user file lwippools.h
  * that defines additional pools beyond the "standard" ones required