diff --git a/libsparse/backed_block.cpp b/libsparse/backed_block.cpp
index 7f5632e..f3d8022 100644
--- a/libsparse/backed_block.cpp
+++ b/libsparse/backed_block.cpp
@@ -133,7 +133,7 @@
                             struct backed_block* start, struct backed_block* end) {
   struct backed_block* bb;
 
-  if (start == NULL) {
+  if (start == nullptr) {
     start = from->data_blocks;
   }
 
@@ -142,12 +142,12 @@
       ;
   }
 
-  if (start == NULL || end == NULL) {
+  if (start == nullptr || end == nullptr) {
     return;
   }
 
-  from->last_used = NULL;
-  to->last_used = NULL;
+  from->last_used = nullptr;
+  to->last_used = nullptr;
   if (from->data_blocks == start) {
     from->data_blocks = end->next;
   } else {
@@ -161,7 +161,7 @@
 
   if (!to->data_blocks) {
     to->data_blocks = start;
-    end->next = NULL;
+    end->next = nullptr;
   } else {
     for (bb = to->data_blocks; bb; bb = bb->next) {
       if (!bb->next || bb->next->block > start->block) {
@@ -230,7 +230,7 @@
 static int queue_bb(struct backed_block_list* bbl, struct backed_block* new_bb) {
   struct backed_block* bb;
 
-  if (bbl->data_blocks == NULL) {
+  if (bbl->data_blocks == nullptr) {
     bbl->data_blocks = new_bb;
     return 0;
   }
@@ -253,7 +253,7 @@
   for (; bb->next && bb->next->block < new_bb->block; bb = bb->next)
     ;
 
-  if (bb->next == NULL) {
+  if (bb->next == nullptr) {
     bb->next = new_bb;
   } else {
     new_bb->next = bb->next;
@@ -273,7 +273,7 @@
 int backed_block_add_fill(struct backed_block_list* bbl, unsigned int fill_val, unsigned int len,
                           unsigned int block) {
   struct backed_block* bb = reinterpret_cast<backed_block*>(calloc(1, sizeof(struct backed_block)));
-  if (bb == NULL) {
+  if (bb == nullptr) {
     return -ENOMEM;
   }
 
@@ -281,7 +281,7 @@
   bb->len = len;
   bb->type = BACKED_BLOCK_FILL;
   bb->fill.val = fill_val;
-  bb->next = NULL;
+  bb->next = nullptr;
 
   return queue_bb(bbl, bb);
 }
@@ -290,7 +290,7 @@
 int backed_block_add_data(struct backed_block_list* bbl, void* data, unsigned int len,
                           unsigned int block) {
   struct backed_block* bb = reinterpret_cast<backed_block*>(calloc(1, sizeof(struct backed_block)));
-  if (bb == NULL) {
+  if (bb == nullptr) {
     return -ENOMEM;
   }
 
@@ -298,7 +298,7 @@
   bb->len = len;
   bb->type = BACKED_BLOCK_DATA;
   bb->data.data = data;
-  bb->next = NULL;
+  bb->next = nullptr;
 
   return queue_bb(bbl, bb);
 }
@@ -307,7 +307,7 @@
 int backed_block_add_file(struct backed_block_list* bbl, const char* filename, int64_t offset,
                           unsigned int len, unsigned int block) {
   struct backed_block* bb = reinterpret_cast<backed_block*>(calloc(1, sizeof(struct backed_block)));
-  if (bb == NULL) {
+  if (bb == nullptr) {
     return -ENOMEM;
   }
 
@@ -316,7 +316,7 @@
   bb->type = BACKED_BLOCK_FILE;
   bb->file.filename = strdup(filename);
   bb->file.offset = offset;
-  bb->next = NULL;
+  bb->next = nullptr;
 
   return queue_bb(bbl, bb);
 }
@@ -325,7 +325,7 @@
 int backed_block_add_fd(struct backed_block_list* bbl, int fd, int64_t offset, unsigned int len,
                         unsigned int block) {
   struct backed_block* bb = reinterpret_cast<backed_block*>(calloc(1, sizeof(struct backed_block)));
-  if (bb == NULL) {
+  if (bb == nullptr) {
     return -ENOMEM;
   }
 
@@ -334,7 +334,7 @@
   bb->type = BACKED_BLOCK_FD;
   bb->fd.fd = fd;
   bb->fd.offset = offset;
-  bb->next = NULL;
+  bb->next = nullptr;
 
   return queue_bb(bbl, bb);
 }
@@ -350,7 +350,7 @@
   }
 
   new_bb = reinterpret_cast<backed_block*>(malloc(sizeof(struct backed_block)));
-  if (new_bb == NULL) {
+  if (new_bb == nullptr) {
     return -ENOMEM;
   }
 
diff --git a/libsparse/output_file.cpp b/libsparse/output_file.cpp
index 5388e77..fe314b3 100644
--- a/libsparse/output_file.cpp
+++ b/libsparse/output_file.cpp
@@ -233,7 +233,7 @@
   while (len > 0) {
     ret = gzwrite(outgz->gz_fd, data, min(len, (unsigned int)INT_MAX));
     if (ret == 0) {
-      error("gzwrite %s", gzerror(outgz->gz_fd, NULL));
+      error("gzwrite %s", gzerror(outgz->gz_fd, nullptr));
       return -1;
     }
     len -= ret;
@@ -269,7 +269,7 @@
 
   while (off > 0) {
     to_write = min(off, (int64_t)INT_MAX);
-    ret = outc->write(outc->priv, NULL, to_write);
+    ret = outc->write(outc->priv, nullptr, to_write);
     if (ret < 0) {
       return ret;
     }
@@ -568,7 +568,7 @@
       reinterpret_cast<struct output_file_gz*>(calloc(1, sizeof(struct output_file_gz)));
   if (!outgz) {
     error_errno("malloc struct outgz");
-    return NULL;
+    return nullptr;
   }
 
   outgz->out.ops = &gz_file_ops;
@@ -581,7 +581,7 @@
       reinterpret_cast<struct output_file_normal*>(calloc(1, sizeof(struct output_file_normal)));
   if (!outn) {
     error_errno("malloc struct outn");
-    return NULL;
+    return nullptr;
   }
 
   outn->out.ops = &file_ops;
@@ -599,7 +599,7 @@
       reinterpret_cast<struct output_file_callback*>(calloc(1, sizeof(struct output_file_callback)));
   if (!outc) {
     error_errno("malloc struct outc");
-    return NULL;
+    return nullptr;
   }
 
   outc->out.ops = &callback_file_ops;
@@ -609,7 +609,7 @@
   ret = output_file_init(&outc->out, block_size, len, sparse, chunks, crc);
   if (ret < 0) {
     free(outc);
-    return NULL;
+    return nullptr;
   }
 
   return &outc->out;
@@ -626,7 +626,7 @@
     out = output_file_new_normal();
   }
   if (!out) {
-    return NULL;
+    return nullptr;
   }
 
   out->ops->open(out, fd);
@@ -634,7 +634,7 @@
   ret = output_file_init(out, block_size, len, sparse, chunks, crc);
   if (ret < 0) {
     free(out);
-    return NULL;
+    return nullptr;
   }
 
   return out;
@@ -664,7 +664,7 @@
 #ifndef _WIN32
   if (buffer_size > SIZE_MAX) return -E2BIG;
   char* data =
-      reinterpret_cast<char*>(mmap64(NULL, buffer_size, PROT_READ, MAP_SHARED, fd, aligned_offset));
+      reinterpret_cast<char*>(mmap64(nullptr, buffer_size, PROT_READ, MAP_SHARED, fd, aligned_offset));
   if (data == MAP_FAILED) {
     return -errno;
   }
diff --git a/libsparse/simg2simg.cpp b/libsparse/simg2simg.cpp
index 7e65701..a2c296e 100644
--- a/libsparse/simg2simg.cpp
+++ b/libsparse/simg2simg.cpp
@@ -66,7 +66,7 @@
     exit(-1);
   }
 
-  files = sparse_file_resparse(s, max_size, NULL, 0);
+  files = sparse_file_resparse(s, max_size, nullptr, 0);
   if (files < 0) {
     fprintf(stderr, "Failed to resparse\n");
     exit(-1);
diff --git a/libsparse/sparse.cpp b/libsparse/sparse.cpp
index 6ff97b6..cb288c5 100644
--- a/libsparse/sparse.cpp
+++ b/libsparse/sparse.cpp
@@ -30,13 +30,13 @@
 struct sparse_file* sparse_file_new(unsigned int block_size, int64_t len) {
   struct sparse_file* s = reinterpret_cast<sparse_file*>(calloc(sizeof(struct sparse_file), 1));
   if (!s) {
-    return NULL;
+    return nullptr;
   }
 
   s->backed_block_list = backed_block_list_new(block_size);
   if (!s->backed_block_list) {
     free(s);
-    return NULL;
+    return nullptr;
   }
 
   s->block_size = block_size;
@@ -252,7 +252,7 @@
                                                   unsigned int len) {
   int64_t count = 0;
   struct output_file* out_counter;
-  struct backed_block* last_bb = NULL;
+  struct backed_block* last_bb = nullptr;
   struct backed_block* bb;
   struct backed_block* start;
   unsigned int last_block = 0;
@@ -270,7 +270,7 @@
   out_counter = output_file_open_callback(out_counter_write, &count, to->block_size, to->len, false,
                                           true, 0, false);
   if (!out_counter) {
-    return NULL;
+    return nullptr;
   }
 
   for (bb = start; bb; bb = backed_block_iter_next(bb)) {
@@ -281,7 +281,7 @@
     /* will call out_counter_write to update count */
     ret = sparse_file_write_block(out_counter, bb);
     if (ret) {
-      bb = NULL;
+      bb = nullptr;
       goto out;
     }
     if (file_len + count > len) {
@@ -330,13 +330,13 @@
     if (c < out_s_count) {
       out_s[c] = s;
     } else {
-      backed_block_list_move(s->backed_block_list, tmp->backed_block_list, NULL, NULL);
+      backed_block_list_move(s->backed_block_list, tmp->backed_block_list, nullptr, nullptr);
       sparse_file_destroy(s);
     }
     c++;
   } while (bb);
 
-  backed_block_list_move(tmp->backed_block_list, in_s->backed_block_list, NULL, NULL);
+  backed_block_list_move(tmp->backed_block_list, in_s->backed_block_list, nullptr, nullptr);
 
   sparse_file_destroy(tmp);
 
diff --git a/libsparse/sparse_read.cpp b/libsparse/sparse_read.cpp
index 56e2c9a..c4c1823 100644
--- a/libsparse/sparse_read.cpp
+++ b/libsparse/sparse_read.cpp
@@ -276,7 +276,7 @@
     return ret;
   }
 
-  if (crc32 != NULL && file_crc32 != *crc32) {
+  if (crc32 != nullptr && file_crc32 != *crc32) {
     return -EINVAL;
   }
 
@@ -339,7 +339,7 @@
   sparse_header_t sparse_header;
   chunk_header_t chunk_header;
   uint32_t crc32 = 0;
-  uint32_t* crc_ptr = 0;
+  uint32_t* crc_ptr = nullptr;
   unsigned int cur_block = 0;
 
   if (!copybuf) {
@@ -489,39 +489,39 @@
   ret = source->ReadValue(&sparse_header, sizeof(sparse_header));
   if (ret < 0) {
     verbose_error(verbose, ret, "header");
-    return NULL;
+    return nullptr;
   }
 
   if (sparse_header.magic != SPARSE_HEADER_MAGIC) {
     verbose_error(verbose, -EINVAL, "header magic");
-    return NULL;
+    return nullptr;
   }
 
   if (sparse_header.major_version != SPARSE_HEADER_MAJOR_VER) {
     verbose_error(verbose, -EINVAL, "header major version");
-    return NULL;
+    return nullptr;
   }
 
   if (sparse_header.file_hdr_sz < SPARSE_HEADER_LEN) {
-    return NULL;
+    return nullptr;
   }
 
   if (sparse_header.chunk_hdr_sz < sizeof(chunk_header_t)) {
-    return NULL;
+    return nullptr;
   }
 
   len = (int64_t)sparse_header.total_blks * sparse_header.blk_sz;
   s = sparse_file_new(sparse_header.blk_sz, len);
   if (!s) {
-    verbose_error(verbose, -EINVAL, NULL);
-    return NULL;
+    verbose_error(verbose, -EINVAL, nullptr);
+    return nullptr;
   }
 
   ret = source->SetOffset(0);
   if (ret < 0) {
     verbose_error(verbose, ret, "seeking");
     sparse_file_destroy(s);
-    return NULL;
+    return nullptr;
   }
 
   s->verbose = verbose;
@@ -529,7 +529,7 @@
   ret = sparse_file_read_sparse(s, source, crc);
   if (ret < 0) {
     sparse_file_destroy(s);
-    return NULL;
+    return nullptr;
   }
 
   return s;
@@ -557,20 +557,20 @@
 
   len = lseek64(fd, 0, SEEK_END);
   if (len < 0) {
-    return NULL;
+    return nullptr;
   }
 
   lseek64(fd, 0, SEEK_SET);
 
   s = sparse_file_new(4096, len);
   if (!s) {
-    return NULL;
+    return nullptr;
   }
 
   ret = sparse_file_read_normal(s, fd);
   if (ret < 0) {
     sparse_file_destroy(s);
-    return NULL;
+    return nullptr;
   }
 
   return s;