diff --git a/rtgui/histogrampanel.cc b/rtgui/histogrampanel.cc
index 9123e7841..6bda0812e 100644
--- a/rtgui/histogrampanel.cc
+++ b/rtgui/histogrampanel.cc
@@ -1181,7 +1181,8 @@ void HistogramArea::update(
                 bhistRaw = histBlueRaw;
                 break;
             case ScopeType::PARADE:
-            case ScopeType::WAVEFORM:
+            case ScopeType::WAVEFORM: {
+                MyWriterLock wave_lock(wave_mutex);
                 waveform_scale = waveformScale;
                 rwave = waveformRed;
                 gwave = waveformGreen;
@@ -1189,6 +1190,7 @@ void HistogramArea::update(
                 lwave = waveformLuma;
                 parade_buffer_r_dirty = parade_buffer_g_dirty = parade_buffer_b_dirty = wave_buffer_dirty = wave_buffer_luma_dirty = true;
                 break;
+            }
             case ScopeType::VECTORSCOPE_HS:
                 vectorscope_scale = vectorscopeScale;
                 vect_hs = vectorscopeHS;
@@ -1313,6 +1315,7 @@ void HistogramArea::updateBackBuffer ()
 
     cr->unset_dash();
 
+    MyReaderLock wave_lock(wave_mutex);
     if (valid && (scopeType == ScopeType::HISTOGRAM || scopeType == ScopeType::HISTOGRAM_RAW)) {
         bool rawMode = scopeType == ScopeType::HISTOGRAM_RAW;
 
@@ -1429,6 +1432,7 @@ void HistogramArea::updateBackBuffer ()
     } else if (scopeType == ScopeType::VECTORSCOPE_HC || scopeType == ScopeType::VECTORSCOPE_HS) {
         drawVectorscope(cr, w, h);
     }
+    wave_lock.release();
 
     // Draw the frame's border
     style->render_frame(cr, 0, 0, surface->get_width(), surface->get_height());
diff --git a/rtgui/histogrampanel.h b/rtgui/histogrampanel.h
index 393df51a5..26b744546 100644
--- a/rtgui/histogrampanel.h
+++ b/rtgui/histogrampanel.h
@@ -169,6 +169,7 @@ protected:
     bool vect_hc_buffer_dirty, vect_hs_buffer_dirty;
     int waveform_scale;
     array2D<int> rwave, gwave, bwave, lwave;
+    MyRWMutex wave_mutex;
     std::vector<unsigned char> parade_buffer_r;
     std::vector<unsigned char> parade_buffer_g;
     std::vector<unsigned char> parade_buffer_b;