diff --git a/src/386_dynarec.c b/src/386_dynarec.c
index 7411ad3..144177e 100644
--- a/src/386_dynarec.c
+++ b/src/386_dynarec.c
@@ -612,7 +612,7 @@ void exec386_dynarec(int cycs)
                         {
                                 codegen_check_flush(page, page->dirty_mask[(phys_addr >> 10) & 3], phys_addr);
                                 page->dirty_mask[(phys_addr >> 10) & 3] = 0;
-                                if (!block->pc)
+                                if (block->pc == BLOCK_PC_INVALID)
                                         valid_block = 0;
                         }
                         if (valid_block && block->page_mask2)
@@ -632,7 +632,7 @@ void exec386_dynarec(int cycs)
                                 {
                                         codegen_check_flush(page_2, page_2->dirty_mask[(phys_addr_2 >> 10) & 3], phys_addr_2);
                                         page_2->dirty_mask[(phys_addr_2 >> 10) & 3] = 0;
-                                        if (!block->pc)
+                                        if (block->pc == BLOCK_PC_INVALID)
                                                 valid_block = 0;
                                 }
                         }
diff --git a/src/codegen.h b/src/codegen.h
index 8eaab36..3a8a955 100644
--- a/src/codegen.h
+++ b/src/codegen.h
@@ -74,6 +74,8 @@ typedef struct codeblock_t
 /*Code block is always entered with the same FPU top-of-stack*/
 #define CODEBLOCK_STATIC_TOP 2
 
+#define BLOCK_PC_INVALID 0xffffffff
+
 static inline codeblock_t *codeblock_tree_find(uint32_t phys, uint32_t _cs)
 {
         codeblock_t *block = pages[phys >> 12].head;
diff --git a/src/codegen_x86-64.c b/src/codegen_x86-64.c
index 7220966..0c21a3a 100644
--- a/src/codegen_x86-64.c
+++ b/src/codegen_x86-64.c
@@ -61,6 +61,8 @@ static int last_ssegs;
 
 void codegen_init()
 {
+        int c;
+
 #ifdef __linux__
 	void *start;
 	size_t len;
@@ -78,6 +80,9 @@ void codegen_init()
         memset(codeblock, 0, BLOCK_SIZE * sizeof(codeblock_t));
         memset(codeblock_hash, 0, HASH_SIZE * sizeof(codeblock_t *));
 
+        for (c = 0; c < BLOCK_SIZE; c++)
+                codeblock[c].pc = BLOCK_PC_INVALID;
+
 #ifdef __linux__
 	start = (void *)((long)codeblock & pagemask);
 	len = ((BLOCK_SIZE * sizeof(codeblock_t)) + pagesize) & pagemask;
@@ -92,9 +97,14 @@ void codegen_init()
 
 void codegen_reset()
 {
+        int c;
+        
         memset(codeblock, 0, BLOCK_SIZE * sizeof(codeblock_t));
         memset(codeblock_hash, 0, HASH_SIZE * sizeof(codeblock_t *));
         mem_reset_page_blocks();
+
+        for (c = 0; c < BLOCK_SIZE; c++)
+                codeblock[c].pc = BLOCK_PC_INVALID;
 }
 
 void dump_block()
@@ -136,8 +146,8 @@ static void add_to_block_list(codeblock_t *block)
 
         if (block->next)
         {
-                if (!block->next->pc)
-                        fatal("block->next->pc=0 %p %p %x %x\n", (void *)block->next, (void *)codeblock, block_current, block_pos);
+                if (block->next->pc == BLOCK_PC_INVALID)
+                        fatal("block->next->pc=BLOCK_PC_INVALID %p %p %x %x\n", (void *)block->next, (void *)codeblock, block_current, block_pos);
         }
         
         if (block->page_mask2)
@@ -208,9 +218,9 @@ static void delete_block(codeblock_t *block)
         if (block == codeblock_hash[HASH(block->phys)])
                 codeblock_hash[HASH(block->phys)] = NULL;
 
-        if (!block->pc)
+        if (block->pc == BLOCK_PC_INVALID)
                 fatal("Deleting deleted block\n");
-        block->pc = 0;
+        block->pc = BLOCK_PC_INVALID;
 
         codeblock_tree_delete(block);
         remove_from_block_list(block, old_pc);
@@ -260,7 +270,7 @@ void codegen_block_init(uint32_t phys_addr)
 
 //        if (block->pc == 0xb00b4ff5)
 //                pclog("Init target block\n");
-        if (block->pc != 0)
+        if (block->pc != BLOCK_PC_INVALID)
         {
 //                pclog("Reuse block : was %08x now %08x\n", block->pc, cs+pc);
                 delete_block(block);
@@ -453,8 +463,8 @@ void codegen_block_generate_end_mask()
                         if (block->next_2)
                         {
 //                        pclog("  next_2->pc=%08x\n", block->next_2->pc);
-                                if (!block->next_2->pc)
-                                        fatal("block->next_2->pc=0 %p\n", (void *)block->next_2);
+                                if (block->next_2->pc == BLOCK_PC_INVALID)
+                                        fatal("block->next_2->pc=BLOCK_PC_INVALID %p\n", (void *)block->next_2);
                         }
                         
                         block->dirty_mask2 = &page_2->dirty_mask[(block->phys_2 >> PAGE_MASK_INDEX_SHIFT) & PAGE_MASK_INDEX_MASK];
diff --git a/src/codegen_x86.c b/src/codegen_x86.c
index 14f076e..688a363 100644
--- a/src/codegen_x86.c
+++ b/src/codegen_x86.c
@@ -1123,6 +1123,7 @@ static uint32_t gen_MEM_CHECK_WRITE_L()
 
 void codegen_init()
 {
+        int c;
 #ifdef __linux__
 	void *start;
 	size_t len;
@@ -1140,6 +1141,9 @@ void codegen_init()
         memset(codeblock, 0, (BLOCK_SIZE+1) * sizeof(codeblock_t));
         memset(codeblock_hash, 0, HASH_SIZE * sizeof(codeblock_t *));
 
+        for (c = 0; c < BLOCK_SIZE; c++)
+                codeblock[c].pc = BLOCK_PC_INVALID;
+
 #ifdef __linux__
 	start = (void *)((long)codeblock & pagemask);
 	len = (((BLOCK_SIZE+1) * sizeof(codeblock_t)) + pagesize) & pagemask;
@@ -1205,9 +1209,14 @@ void codegen_init()
 
 void codegen_reset()
 {
+        int c;
+        
         memset(codeblock, 0, BLOCK_SIZE * sizeof(codeblock_t));
         memset(codeblock_hash, 0, HASH_SIZE * sizeof(codeblock_t *));
         mem_reset_page_blocks();
+        
+        for (c = 0; c < BLOCK_SIZE; c++)
+                codeblock[c].pc = BLOCK_PC_INVALID;
 }
 
 void dump_block()
@@ -1249,8 +1258,8 @@ static void add_to_block_list(codeblock_t *block)
 
         if (block->next)
         {
-                if (!block->next->pc)
-                        fatal("block->next->pc=0 %p %p %x %x\n", (void *)block->next, (void *)codeblock, block_current, block_pos);
+                if (block->next->pc == BLOCK_PC_INVALID)
+                        fatal("block->next->pc=BLOCK_PC_INVALID %p %p %x %x\n", (void *)block->next, (void *)codeblock, block_current, block_pos);
         }
         
         if (block->page_mask2)
@@ -1321,9 +1330,9 @@ static void delete_block(codeblock_t *block)
         if (block == codeblock_hash[HASH(block->phys)])
                 codeblock_hash[HASH(block->phys)] = NULL;
 
-        if (!block->pc)
+        if (block->pc == BLOCK_PC_INVALID)
                 fatal("Deleting deleted block\n");
-        block->pc = 0;
+        block->pc = BLOCK_PC_INVALID;
 
         codeblock_tree_delete(block);
         remove_from_block_list(block, old_pc);
@@ -1373,7 +1382,7 @@ void codegen_block_init(uint32_t phys_addr)
 
 //        if (block->pc == 0xb00b4ff5)
 //                pclog("Init target block\n");
-        if (block->pc != 0)
+        if (block->pc != BLOCK_PC_INVALID)
         {
 //                pclog("Reuse block : was %08x now %08x\n", block->pc, cs+pc);
                 delete_block(block);
@@ -1540,8 +1549,8 @@ void codegen_block_generate_end_mask()
                         if (block->next_2)
                         {
 //                        pclog("  next_2->pc=%08x\n", block->next_2->pc);
-                                if (!block->next_2->pc)
-                                        fatal("block->next_2->pc=0 %p\n", (void *)block->next_2);
+                                if (block->next_2->pc == BLOCK_PC_INVALID)
+                                        fatal("block->next_2->pc=BLOCK_PC_INVALID %p\n", (void *)block->next_2);
                         }
 
                         block->dirty_mask2 = &page_2->dirty_mask[(block->phys_2 >> PAGE_MASK_INDEX_SHIFT) & PAGE_MASK_INDEX_MASK];