diff --git a/generator/nanopb_generator.py b/generator/nanopb_generator.py
index 973c7610fbea38337b9792838d0efc2f2987c5dc..185a97bbd2acd539795aaa252d51af0225db99e2 100755
--- a/generator/nanopb_generator.py
+++ b/generator/nanopb_generator.py
@@ -258,16 +258,18 @@ class Field:
 
         # Check field rules, i.e. required/optional/repeated.
         can_be_static = True
-        if desc.label == FieldD.LABEL_REQUIRED:
-            self.rules = 'REQUIRED'
-        elif desc.label == FieldD.LABEL_OPTIONAL:
-            self.rules = 'OPTIONAL'
-        elif desc.label == FieldD.LABEL_REPEATED:
+        if desc.label == FieldD.LABEL_REPEATED:
             self.rules = 'REPEATED'
             if self.max_count is None:
                 can_be_static = False
             else:
                 self.array_decl = '[%d]' % self.max_count
+        elif field_options.HasField("proto3"):
+            self.rules = 'SINGULAR'
+        elif desc.label == FieldD.LABEL_REQUIRED:
+            self.rules = 'REQUIRED'
+        elif desc.label == FieldD.LABEL_OPTIONAL:
+            self.rules = 'OPTIONAL'
         else:
             raise NotImplementedError(desc.label)
 
diff --git a/generator/proto/nanopb.proto b/generator/proto/nanopb.proto
index 8aab19a1b5e88cd2bb34a1081ce12ba5dca849c8..b9961c88d32ccc7bf54463cb2dae694565cf4b6c 100644
--- a/generator/proto/nanopb.proto
+++ b/generator/proto/nanopb.proto
@@ -66,6 +66,9 @@ message NanoPBOptions {
 
   // decode oneof as anonymous union
   optional bool anonymous_oneof = 11 [default = false];
+
+  // Proto3 singular field does not generate a "has_" flag
+  optional bool proto3 = 12 [default = false];
 }
 
 // Extensions to protoc 'Descriptor' type in order to define options
diff --git a/pb.h b/pb.h
index 4576f79abca9bc03c0f97e9e5eb4a4c4262bbe9a..0e1e92d51cdcdbe4b9a8527a850af7ce57988f5d 100644
--- a/pb.h
+++ b/pb.h
@@ -413,6 +413,10 @@ struct pb_extension_s {
     pb_delta(st, has_ ## m, m), \
     pb_membersize(st, m), 0, ptr}
 
+#define PB_SINGULAR_STATIC(tag, st, m, fd, ltype, ptr) \
+    {tag, PB_ATYPE_STATIC | PB_HTYPE_OPTIONAL | ltype, \
+    fd, 0, pb_membersize(st, m), 0, ptr}
+
 /* Repeated fields have a _count field and also the maximum number of entries. */
 #define PB_REPEATED_STATIC(tag, st, m, fd, ltype, ptr) \
     {tag, PB_ATYPE_STATIC | PB_HTYPE_REPEATED | ltype, \
@@ -444,6 +448,11 @@ struct pb_extension_s {
     {tag, PB_ATYPE_POINTER | PB_HTYPE_OPTIONAL | ltype, \
     fd, 0, pb_membersize(st, m[0]), 0, ptr}
 
+/* Same as optional fields*/
+#define PB_SINGULAR_POINTER(tag, st, m, fd, ltype, ptr) \
+    {tag, PB_ATYPE_POINTER | PB_HTYPE_OPTIONAL | ltype, \
+    fd, 0, pb_membersize(st, m[0]), 0, ptr}
+
 /* Repeated fields have a _count field and a pointer to array of pointers */
 #define PB_REPEATED_POINTER(tag, st, m, fd, ltype, ptr) \
     {tag, PB_ATYPE_POINTER | PB_HTYPE_REPEATED | ltype, \
@@ -458,6 +467,10 @@ struct pb_extension_s {
 #define PB_OPTIONAL_CALLBACK(tag, st, m, fd, ltype, ptr) \
     {tag, PB_ATYPE_CALLBACK | PB_HTYPE_OPTIONAL | ltype, \
     fd, 0, pb_membersize(st, m), 0, ptr}
+
+#define PB_SINGULAR_CALLBACK(tag, st, m, fd, ltype, ptr) \
+    {tag, PB_ATYPE_CALLBACK | PB_HTYPE_OPTIONAL | ltype, \
+    fd, 0, pb_membersize(st, m), 0, ptr}
     
 #define PB_REPEATED_CALLBACK(tag, st, m, fd, ltype, ptr) \
     {tag, PB_ATYPE_CALLBACK | PB_HTYPE_REPEATED | ltype, \
diff --git a/pb_decode.c b/pb_decode.c
index 7a4e29a8fda2cb8de68fab47cf31cd1bf6c396f9..1f6aeae0d87dedb4be0e594324b15e71ff98b3c5 100644
--- a/pb_decode.c
+++ b/pb_decode.c
@@ -360,7 +360,8 @@ static bool checkreturn decode_static_field(pb_istream_t *stream, pb_wire_type_t
             return func(stream, iter->pos, iter->pData);
             
         case PB_HTYPE_OPTIONAL:
-            *(bool*)iter->pSize = true;
+            if (iter->pSize != iter->pData)
+                *(bool*)iter->pSize = true;
             return func(stream, iter->pos, iter->pData);
     
         case PB_HTYPE_REPEATED: