diff --git a/main.cpp b/main.cpp
index 6ea1724..e7fe4d4 100644
--- a/main.cpp
+++ b/main.cpp
@@ -71,11 +71,12 @@ static void poh_thread()
 {
     std::vector<float> block_mag(block_len);
 
+    poh_accept_input = true; // accept first block
     while(!shutdown_threads) {
-        poh_accept_input = true;
         poh_input_ready.acquire();
 
         fft_mag(poh_input_block, block_mag.data(), block_len);
+        poh_accept_input = true; // poh_input_block not used again until next iteration
 
         // stabilize laser
         float freq_peak_local;
@@ -107,10 +108,11 @@ static void ls_thread()
 {
     std::vector<float> block_mag(block_len);
 
+    ls_accept_input = true;
     while(!shutdown_threads) {
-        ls_accept_input = true;
         ls_input_ready.acquire();
         fft_mag(ls_input_block, block_mag.data(), block_len);
+        ls_accept_input = true;
         {
             std::lock_guard<std::mutex> guard(wf_ls_mutex);
             std::memmove(&wf_ls[wf_width], &wf_ls[0], sizeof(int)*wf_width*(wf_height - 1));