diff --git a/include/private/error.h b/include/private/error.h
index 1eb9711..27dcfb8 100644
--- a/include/private/error.h
+++ b/include/private/error.h
@@ -27,6 +27,7 @@ enum {
 
     /* Memory Protection Errors */
     ERR_STACK_CHECK, /* Stack overflow or corruption detected */
+    ERR_HEAP_CORRUPT, /* Heap corruption or invalid free detected */
 
     /* IPC and Synchronization Errors */
     ERR_PIPE_ALLOC,    /* Pipe allocation failed */
diff --git a/kernel/error.c b/kernel/error.c
index 1d6071e..4edb49d 100644
--- a/kernel/error.c
+++ b/kernel/error.c
@@ -22,6 +22,7 @@ static const struct error_code error_desc[] = {
 
     /* stack guard */
     {ERR_STACK_CHECK, "stack corruption"},
+    {ERR_HEAP_CORRUPT, "heap corruption or invalid free"},
 
     /* IPC / sync */
     {ERR_PIPE_ALLOC, "pipe allocation"},
diff --git a/lib/malloc.c b/lib/malloc.c
index ac439ab..f893d3b 100644
--- a/lib/malloc.c
+++ b/lib/malloc.c
@@ -4,6 +4,7 @@
 #include <sys/task.h>
 #include <types.h>
 
+#include "private/error.h"
 #include "private/utils.h"
 
 /* Memory allocator using first-fit strategy with selective coalescing.
@@ -44,15 +45,21 @@ static uint32_t free_blocks_count; /* track fragmentation */
 /* Validate block integrity */
 static inline bool validate_block(memblock_t *block)
 {
-    if (!IS_VALID_BLOCK(block))
+    if (unlikely(!IS_VALID_BLOCK(block)))
         return false;
 
     size_t size = GET_SIZE(block);
-    if (!size || size > MALLOC_MAX_SIZE)
+    if (unlikely(!size || size > MALLOC_MAX_SIZE))
         return false;
 
     /* Check if block extends beyond heap */
-    if ((uint8_t *) block + sizeof(memblock_t) + size > (uint8_t *) heap_end)
+    if (unlikely((uint8_t *) block + sizeof(memblock_t) + size >
+                 (uint8_t *) heap_end))
+        return false;
+
+    if (unlikely(block->next &&
+                 (uint8_t *) block + sizeof(memblock_t) + GET_SIZE(block) !=
+                     (uint8_t *) block->next))
         return false;
 
     return true;
@@ -69,8 +76,9 @@ void free(void *ptr)
     memblock_t *p = ((memblock_t *) ptr) - 1;
 
     /* Validate the block being freed */
-    if (!validate_block(p) || !IS_USED(p)) {
+    if (unlikely(!validate_block(p) || !IS_USED(p))) {
         CRITICAL_LEAVE();
+        panic(ERR_HEAP_CORRUPT);
         return; /* Invalid or double-free */
     }
 
@@ -78,9 +86,7 @@ void free(void *ptr)
     free_blocks_count++;
 
     /* Forward merge if the next block is free and physically adjacent */
-    if (p->next && !IS_USED(p->next) &&
-        (uint8_t *) p + sizeof(memblock_t) + GET_SIZE(p) ==
-            (uint8_t *) p->next) {
+    if (p->next && !IS_USED(p->next)) {
         p->size = GET_SIZE(p) + sizeof(memblock_t) + GET_SIZE(p->next);
         p->next = p->next->next;
         free_blocks_count--;
@@ -94,9 +100,12 @@ void free(void *ptr)
         current = current->next;
     }
 
-    if (prev && !IS_USED(prev) &&
-        (uint8_t *) prev + sizeof(memblock_t) + GET_SIZE(prev) ==
-            (uint8_t *) p) {
+    if (prev && !IS_USED(prev)) {
+        if (unlikely(!validate_block(prev))) {
+            CRITICAL_LEAVE();
+            panic(ERR_HEAP_CORRUPT);
+            return;
+        }
         prev->size = GET_SIZE(prev) + sizeof(memblock_t) + GET_SIZE(p);
         prev->next = p->next;
         free_blocks_count--;
@@ -109,15 +118,16 @@ void free(void *ptr)
 static void selective_coalesce(void)
 {
     memblock_t *p = first_free;
-    uint32_t coalesced = 0;
 
     while (p && p->next) {
         /* Merge only when blocks are FREE *and* adjacent in memory */
-        uint8_t *pend = (uint8_t *) p + sizeof(memblock_t) + GET_SIZE(p);
-        if (!IS_USED(p) && !IS_USED(p->next) && pend == (uint8_t *) p->next) {
+        if (unlikely(!validate_block(p))) {
+            panic(ERR_HEAP_CORRUPT);
+            return;
+        }
+        if (!IS_USED(p) && !IS_USED(p->next)) {
             p->size = GET_SIZE(p) + sizeof(memblock_t) + GET_SIZE(p->next);
             p->next = p->next->next;
-            coalesced++;
             free_blocks_count--;
         } else {
             p = p->next;
@@ -125,6 +135,28 @@ static void selective_coalesce(void)
     }
 }
 
+static inline void split_block(memblock_t *block, size_t size)
+{
+    size_t remaining;
+    memblock_t *new_block;
+
+    if (unlikely(size >= GET_SIZE(block))) {
+        panic(ERR_HEAP_CORRUPT);
+        return;
+    }
+    remaining = GET_SIZE(block) - size;
+    /* Split only when remaining memory is large enough */
+    if (remaining < sizeof(memblock_t) + MALLOC_MIN_SIZE)
+        return;
+    new_block = (memblock_t *) ((size_t) block + sizeof(memblock_t) + size);
+    new_block->next = block->next;
+    new_block->size = remaining - sizeof(memblock_t);
+    MARK_FREE(new_block);
+    block->next = new_block;
+    block->size = size | IS_USED(block);
+    free_blocks_count++; /* New free block created */
+}
+
 /* O(n) first-fit allocation with selective coalescing */
 void *malloc(uint32_t size)
 {
@@ -146,29 +178,22 @@ void *malloc(uint32_t size)
 
     memblock_t *p = first_free;
     while (p) {
-        if (!validate_block(p)) {
+        if (unlikely(!validate_block(p))) {
             CRITICAL_LEAVE();
+            panic(ERR_HEAP_CORRUPT);
             return NULL; /* Heap corruption detected */
         }
 
         if (!IS_USED(p) && GET_SIZE(p) >= size) {
-            size_t remaining = GET_SIZE(p) - size;
-
             /* Split block only if remainder is large enough to be useful */
-            if (remaining >= sizeof(memblock_t) + MALLOC_MIN_SIZE) {
-                memblock_t *new_block =
-                    (memblock_t *) ((size_t) p + sizeof(memblock_t) + size);
-                new_block->next = p->next;
-                new_block->size = remaining - sizeof(memblock_t);
-                MARK_FREE(new_block);
-                p->next = new_block;
-                p->size = size;
-                free_blocks_count++; /* New free block created */
-            }
+            split_block(p, size);
 
             MARK_USED(p);
-            if (free_blocks_count > 0)
-                free_blocks_count--;
+            if (unlikely(free_blocks_count <= 0)) {
+                panic(ERR_HEAP_CORRUPT);
+                return NULL;
+            }
+            free_blocks_count--;
 
             CRITICAL_LEAVE();
             return (void *) (p + 1);
@@ -213,7 +238,7 @@ void *calloc(uint32_t nmemb, uint32_t size)
     if (unlikely(nmemb && size > MALLOC_MAX_SIZE / nmemb))
         return NULL;
 
-    uint32_t total_size = nmemb * size;
+    uint32_t total_size = ALIGN4(nmemb * size);
     void *buf = malloc(total_size);
 
     if (buf)
@@ -236,11 +261,15 @@ void *realloc(void *ptr, uint32_t size)
         return NULL;
     }
 
+    size = ALIGN4(size);
+
     memblock_t *old_block = ((memblock_t *) ptr) - 1;
 
     /* Validate the existing block */
-    if (!validate_block(old_block) || !IS_USED(old_block))
+    if (unlikely(!validate_block(old_block) || !IS_USED(old_block))) {
+        panic(ERR_HEAP_CORRUPT);
         return NULL;
+    }
 
     size_t old_size = GET_SIZE(old_block);
 
@@ -249,6 +278,33 @@ void *realloc(void *ptr, uint32_t size)
         old_size - size < sizeof(memblock_t) + MALLOC_MIN_SIZE)
         return ptr;
 
+    /* fast path for shrinking */
+    if (size <= old_size) {
+        split_block(old_block, size);
+        /* Trigger coalescing only when fragmentation is high */
+        if (free_blocks_count > COALESCE_THRESHOLD)
+            selective_coalesce();
+        CRITICAL_LEAVE();
+        return (void *) (old_block + 1);
+    }
+
+    /* fast path for growing */
+    if (old_block->next && !IS_USED(old_block->next) &&
+        GET_SIZE(old_block) + sizeof(memblock_t) + GET_SIZE(old_block->next) >=
+            size) {
+        old_block->size = GET_SIZE(old_block) + sizeof(memblock_t) +
+                          GET_SIZE(old_block->next);
+        old_block->next = old_block->next->next;
+        free_blocks_count--;
+        split_block(old_block, size);
+        /* Trigger coalescing only when fragmentation is high */
+        if (free_blocks_count > COALESCE_THRESHOLD)
+            selective_coalesce();
+        CRITICAL_LEAVE();
+        return (void *) (old_block + 1);
+    }
+
+
     void *new_buf = malloc(size);
     if (new_buf) {
         memcpy(new_buf, ptr, min(old_size, size));