diff --git a/code/userprog/addrspace.cc b/code/userprog/addrspace.cc
index fee6ced..fa9784e 100644
--- a/code/userprog/addrspace.cc
+++ b/code/userprog/addrspace.cc
@@ -132,7 +132,7 @@ AddrSpace::AddrSpace (OpenFile * executable)
     pageTable[0].valid = FALSE;			// Catch NULL dereference
 
     #ifdef CHANGED
-    int bitmapSize = UserStacksAreaSize / UserStackSize;
+    int bitmapSize =( UserStacksAreaSize / UserStackSize)-1;
     DEBUG('x', "Initialise thread counter\n");
     threads = 1;
     
@@ -325,20 +325,26 @@ AddrSpace::AllocateUserStack()
     /* If we don't have any free slot, we can wait for one to be
      * freed by DeAllocateUserstack
      */
-    while ((bit = memoryMap->Find()) == - 1){
-        DEBUG('x', "Can't allocate User Stack Wainting...\n");
-        semAllocateUserStack->P();
+
+    semAllocateUserStack->P();
+    bit = memoryMap->Find();
+    semAllocateUserStack->V();
+    if ( bit == - 1 ) {
+        DEBUG('x', "No slot avaible on User Stack\n");
+        return -1;
     }
     int addr = memory - UserStackSize * bit;
     DEBUG('x', "Allocate User Stack bit %d, addr:%x\n", bit, addr);
     return addr;
 }
+
 void
 AddrSpace::DeAllocateUserStack(int addr){
-    int memory = numPages * PageSize;
+    int memory =  numPages * PageSize;
     int bit = (memory - addr) / UserStackSize;
     DEBUG('x', "Deallocate User Stack bit %d, addr:%x\n", bit, addr);
+    semAllocateUserStack->P();
     memoryMap->Clear(bit);
-    semAllocateUserStack->V();
+    semAllocateUserStack->P();
 }
 #endif
diff --git a/code/userprog/userthread.cc b/code/userprog/userthread.cc
index f1b0aa2..f2eb94e 100644
--- a/code/userprog/userthread.cc
+++ b/code/userprog/userthread.cc
@@ -15,7 +15,6 @@ static void StartUserThread( void * args ){
     // because we only have a void in our function definition
     ThreadArgs_t * cpy_args;
     cpy_args = (ThreadArgs_t *) args;
-    int stack_addr = currentThread->space->AllocateUserStack();
 
     // init register
     for (int i = 0; i < NumTotalRegs; i++ ) {
@@ -32,8 +31,8 @@ static void StartUserThread( void * args ){
     DEBUG('x',"Register 4: 0x%x\n", cpy_args->arg);
 
     // init stack
-    machine->WriteRegister(StackReg, stack_addr);
-    DEBUG('x',"StackRegister: 0x%x\n", stack_addr);
+    machine->WriteRegister(StackReg, cpy_args->stackAddr);
+    DEBUG('x',"StackRegister: 0x%x\n", cpy_args->stackAddr);
 
     // All our registers have values, we can desallocate our cpy_args
     free(cpy_args);
@@ -51,7 +50,13 @@ int do_ThreadCreate(int f, int arg){
     ThreadArgs_t * args = (ThreadArgs_t *) malloc(sizeof(ThreadArgs_t));
     args->f = f;
     args->arg = arg;
-
+    
+    // Check if we can allocate Stack for our son
+    int stackAddr = currentThread->space->AllocateUserStack();
+    if ( stackAddr == -1 ) {
+        fprintf(stderr, "Segmentation Fault - no space avaible on stack\n");
+        Exit(1);
+    }
     // create a new Thread and start it
     Thread * newThread = new Thread("new thread");
 
diff --git a/code/userprog/userthread.h b/code/userprog/userthread.h
index 7510d4c..e49b51b 100644
--- a/code/userprog/userthread.h
+++ b/code/userprog/userthread.h
@@ -6,6 +6,7 @@
 typedef struct {
     int f;
     int arg;
+    int stackAddr;
 } ThreadArgs_t;
 
 extern int do_ThreadCreate(int f, int arg);