diff --git a/context_node.cpp b/context_node.cpp
index 572bf97..18056e9 100644
--- a/context_node.cpp
+++ b/context_node.cpp
@@ -53,7 +53,7 @@ bool ContextNode::Open(bool access_rw, bool* fsetxattr_failed) {
   if (access_rw) {
     pa_ = prop_area::map_prop_area_rw(filename.c_str(), context_, fsetxattr_failed);
   } else {
-    pa_ = prop_area::map_prop_area(filename.c_str());
+    pa_ = prop_area::map_prop_area(filename.c_str(), nullptr);
   }
   lock_.unlock();
   return pa_;
diff --git a/contexts_serialized.cpp b/contexts_serialized.cpp
index 6aabb7f..254a9cc 100644
--- a/contexts_serialized.cpp
+++ b/contexts_serialized.cpp
@@ -70,7 +70,7 @@ bool ContextsSerialized::MapSerialPropertyArea(bool access_rw, bool* fsetxattr_f
     serial_prop_area_ = prop_area::map_prop_area_rw(
         serial_filename_.c_str(), "u:object_r:properties_serial:s0", fsetxattr_failed);
   } else {
-    serial_prop_area_ = prop_area::map_prop_area(serial_filename_.c_str());
+    serial_prop_area_ = prop_area::map_prop_area(serial_filename_.c_str(), &rw_);
   }
   return serial_prop_area_;
 }
diff --git a/contexts_split.cpp b/contexts_split.cpp
index 8317484..dca5132 100644
--- a/contexts_split.cpp
+++ b/contexts_split.cpp
@@ -197,7 +197,7 @@ bool ContextsSplit::MapSerialPropertyArea(bool access_rw, bool* fsetxattr_failed
     serial_prop_area_ = prop_area::map_prop_area_rw(
         filename.c_str(), "u:object_r:properties_serial:s0", fsetxattr_failed);
   } else {
-    serial_prop_area_ = prop_area::map_prop_area(filename.c_str());
+    serial_prop_area_ = prop_area::map_prop_area(filename.c_str(), &rw_);
   }
   return serial_prop_area_;
 }
diff --git a/include/system_properties/contexts.h b/include/system_properties/contexts.h
index df8c5a2..a59c063 100644
--- a/include/system_properties/contexts.h
+++ b/include/system_properties/contexts.h
@@ -43,4 +43,5 @@ class Contexts {
   virtual void ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) = 0;
   virtual void ResetAccess() = 0;
   virtual void FreeAndUnmap() = 0;
+  bool rw_ = false;
 };
diff --git a/include/system_properties/contexts_pre_split.h b/include/system_properties/contexts_pre_split.h
index a6cd039..52f08f9 100644
--- a/include/system_properties/contexts_pre_split.h
+++ b/include/system_properties/contexts_pre_split.h
@@ -39,7 +39,7 @@ class ContextsPreSplit : public Contexts {
 
   // We'll never initialize this legacy option as writable, so don't even check the arg.
   virtual bool Initialize(bool, const char* filename, bool*, bool) override {
-    pre_split_prop_area_ = prop_area::map_prop_area(filename);
+    pre_split_prop_area_ = prop_area::map_prop_area(filename, &rw_);
     return pre_split_prop_area_ != nullptr;
   }
 
diff --git a/include/system_properties/prop_area.h b/include/system_properties/prop_area.h
index 187ff75..f466b58 100644
--- a/include/system_properties/prop_area.h
+++ b/include/system_properties/prop_area.h
@@ -93,7 +93,7 @@ class prop_area {
  public:
   static prop_area* map_prop_area_rw(const char* filename, const char* context,
                                      bool* fsetxattr_failed);
-  static prop_area* map_prop_area(const char* filename);
+  static prop_area* map_prop_area(const char* filename, bool *is_rw);
   static void unmap_prop_area(prop_area** pa) {
     if (*pa) {
       munmap(*pa, pa_size_);
@@ -139,7 +139,7 @@ class prop_area {
   char* dirty_backup_area() { return data_ + sizeof(prop_trie_node); }
 
  private:
-  static prop_area* map_fd_ro(const int fd);
+  static prop_area* map_fd_ro(const int fd, bool rw);
 
   void* allocate_obj(const size_t size, uint_least32_t* const off);
   prop_trie_node* new_prop_trie_node(const char* name, uint32_t namelen, uint_least32_t* const off);
diff --git a/prop_area.cpp b/prop_area.cpp
index 4668eed..318e677 100644
--- a/prop_area.cpp
+++ b/prop_area.cpp
@@ -104,7 +104,7 @@ prop_area* prop_area::map_prop_area_rw(const char* filename, const char* context
   return pa;
 }
 
-prop_area* prop_area::map_fd_ro(const int fd) {
+prop_area* prop_area::map_fd_ro(const int fd, bool rw) {
   struct stat fd_stat;
   if (fstat(fd, &fd_stat) < 0) {
     return nullptr;
@@ -119,7 +119,8 @@ prop_area* prop_area::map_fd_ro(const int fd) {
   pa_size_ = fd_stat.st_size;
   pa_data_size_ = pa_size_ - sizeof(prop_area);
 
-  void* const map_result = mmap(nullptr, pa_size_, PROT_READ, MAP_SHARED, fd, 0);
+  int prot = rw ? PROT_READ | PROT_WRITE : PROT_READ;
+  void* const map_result = mmap(nullptr, pa_size_, prot, MAP_SHARED, fd, 0);
   if (map_result == MAP_FAILED) {
     return nullptr;
   }
@@ -133,13 +134,22 @@ prop_area* prop_area::map_fd_ro(const int fd) {
   return pa;
 }
 
-prop_area* prop_area::map_prop_area(const char* filename) {
-  int fd = open(filename, O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
-  if (fd == -1) return nullptr;
+prop_area* prop_area::map_prop_area(const char* filename, bool *is_rw) {
+  bool rw = false;
+  int fd = open(filename, O_CLOEXEC | O_NOFOLLOW | O_RDWR);
+  if (fd == -1) {
+    fd = open(filename, O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
+    if (fd == -1) {
+      return nullptr;
+    }
+  } else {
+    rw = true;
+  }
 
-  prop_area* map_result = map_fd_ro(fd);
+  prop_area* map_result = map_fd_ro(fd, rw);
   close(fd);
 
+  if (is_rw) *is_rw = rw;
   return map_result;
 }
 
diff --git a/system_properties.cpp b/system_properties.cpp
index 4d3f6b6..7b58852 100644
--- a/system_properties.cpp
+++ b/system_properties.cpp
@@ -276,6 +276,10 @@ int SystemProperties::Update(prop_info* pi, const char* value, unsigned int len)
   }
   bool have_override = appcompat_override_contexts_ != nullptr;
 
+  if (!contexts_->rw_) {
+    return -1;
+  }
+
   prop_area* serial_pa = contexts_->GetSerialPropArea();
   prop_area* override_serial_pa =
       have_override ? appcompat_override_contexts_->GetSerialPropArea() : nullptr;
@@ -355,6 +359,10 @@ int SystemProperties::Add(const char* name, unsigned int namelen, const char* va
     return -1;
   }
 
+  if (!contexts_->rw_) {
+    return -1;
+  }
+
   prop_area* serial_pa = contexts_->GetSerialPropArea();
   if (serial_pa == nullptr) {
     async_safe_format_log(ANDROID_LOG_ERROR, "libc",