3 files changed, 4 insertions, 2 deletions
diff --git a/gnuradio-core/src/lib/runtime/gr_basic_block.h b/gnuradio-core/src/lib/runtime/gr_basic_block.h
index ce7a1aa1d..3b0cd51dd 100644
--- a/gnuradio-core/src/lib/runtime/gr_basic_block.h
+++ b/gnuradio-core/src/lib/runtime/gr_basic_block.h
@@ -73,6 +73,8 @@ protected:
     long                 d_unique_id;
     vcolor               d_color;
 
+    gr_basic_block(void){} //allows pure virtual interface sub-classes
+
     //! Protected constructor prevents instantiation by non-derived classes
     gr_basic_block(const std::string &name,
                    gr_io_signature_sptr input_signature,
diff --git a/gnuradio-core/src/lib/runtime/gr_block.h b/gnuradio-core/src/lib/runtime/gr_block.h
index ad7fa9555..fc22f9ea8 100644
--- a/gnuradio-core/src/lib/runtime/gr_block.h
+++ b/gnuradio-core/src/lib/runtime/gr_block.h
@@ -236,7 +236,7 @@ class gr_block : public gr_basic_block {
   tag_propagation_policy_t d_tag_propagation_policy; // policy for moving tags downstream
     
  protected:
-
+  gr_block (void){} //allows pure virtual interface sub-classes
   gr_block (const std::string &name,
             gr_io_signature_sptr input_signature,
             gr_io_signature_sptr output_signature);
diff --git a/gnuradio-core/src/lib/runtime/gr_sync_block.h b/gnuradio-core/src/lib/runtime/gr_sync_block.h
index 3a5d89d19..c5a6a50f1 100644
--- a/gnuradio-core/src/lib/runtime/gr_sync_block.h
+++ b/gnuradio-core/src/lib/runtime/gr_sync_block.h
@@ -34,7 +34,7 @@
 class gr_sync_block : public gr_block
 {
  protected:
-
+  gr_sync_block (void){} //allows pure virtual interface sub-classes
   gr_sync_block (const std::string &name,
 		 gr_io_signature_sptr input_signature,
 		 gr_io_signature_sptr output_signature);