diff --git a/include/light/light.hh b/include/light/light.hh
index 46b7d624..bfadf83a 100644
--- a/include/light/light.hh
+++ b/include/light/light.hh
@@ -150,6 +150,8 @@ typedef struct {
 
 /* debug */
 
+extern bool debug_highlightseams;
+
 typedef enum {
     debugmode_none = 0,
     debugmode_phong,
diff --git a/light/light.cc b/light/light.cc
index 363d99c6..fd43a195 100644
--- a/light/light.cc
+++ b/light/light.cc
@@ -91,6 +91,7 @@ qboolean onlyents = false;
 qboolean novisapprox = false;
 bool nolights = false;
 backend_t rtbackend = backend_embree;
+bool debug_highlightseams = false;
 debugmode_t debugmode = debugmode_none;
 bool verbose_log = false;
 
@@ -1019,6 +1020,9 @@ light_main(int argc, const char **argv)
             
             CheckNoDebugModeSet();
             debugmode = debugmode_debugneighbours;
+        } else if ( !strcmp( argv[ i ], "-highlightseams" ) ) {
+            logprint("Highlighting lightmap seams\n");
+            debug_highlightseams = true;
         } else if ( !strcmp( argv[ i ], "-verbose" ) ) {
             verbose_log = true;
         } else if ( !strcmp( argv[ i ], "-help" ) ) {
diff --git a/light/ltface.cc b/light/ltface.cc
index d1d88776..17bdaf9b 100644
--- a/light/ltface.cc
+++ b/light/ltface.cc
@@ -2797,9 +2797,13 @@ WriteLightmaps(const mbsp_t *bsp, bsp2_dface_t *face, facesup_t *facesup, const
         for (int t = 0; t < actual_height; t++) {
             for (int s = 0; s < actual_width; s++) {
                 const int sampleindex = (t * actual_width) + s;
-                const qvec4f &color = output_color.at(sampleindex);
+                qvec4f color = output_color.at(sampleindex);
                 const qvec4f &direction = output_dir.at(sampleindex);
                 
+                if (debug_highlightseams && color[3] == 0) {
+                    color = qvec4f(255, 0, 0, 1);
+                }
+                
                 *lit++ = color[0];
                 *lit++ = color[1];
                 *lit++ = color[2];