diff --git a/intern/cycles/scene/light_tree.cpp b/intern/cycles/scene/light_tree.cpp
index 486435048c4..04e34fbda50 100644
--- a/intern/cycles/scene/light_tree.cpp
+++ b/intern/cycles/scene/light_tree.cpp
@@ -108,7 +108,9 @@ LightTreeEmitter::LightTreeEmitter(Scene *scene,
 
     /* TODO: need a better way to handle this when textures are used. */
     float area = triangle_area(vertices[0], vertices[1], vertices[2]);
-    measure.energy = area * average(shader->emission_estimate);
+    /* Use absolute value of emission_estimate so lights with negative strength are properly
+     * supported in the light tree. */
+    measure.energy = area * average(fabs(shader->emission_estimate));
 
     /* NOTE: the original implementation used the bounding box centroid, but triangle centroid
      * seems to work fine */
@@ -220,7 +222,7 @@ LightTreeEmitter::LightTreeEmitter(Scene *scene,
 
     /* Use absolute value of energy so lights with negative strength are properly supported in the
      * light tree. */
-    measure.energy = fabsf(average(strength));
+    measure.energy = average(fabs(strength));
 
     light_set_membership = lamp->get_light_set_membership();
   }
diff --git a/intern/cycles/scene/shader.cpp b/intern/cycles/scene/shader.cpp
index 72db06e2604..6666d2b3b90 100644
--- a/intern/cycles/scene/shader.cpp
+++ b/intern/cycles/scene/shader.cpp
@@ -264,7 +264,7 @@ void Shader::estimate_emission()
   }
 
   ShaderInput *surf = graph->output()->input("Surface");
-  emission_estimate = fabs(output_estimate_emission(surf->link, emission_is_constant));
+  emission_estimate = output_estimate_emission(surf->link, emission_is_constant);
 
   if (is_zero(emission_estimate)) {
     emission_sampling = EMISSION_SAMPLING_NONE;
@@ -274,8 +274,9 @@ void Shader::estimate_emission()
      * using a lot of memory in the light tree and potentially wasting samples
      * where indirect light samples are sufficient.
      * Possible optimization: estimate front and back emission separately. */
-    emission_sampling = (reduce_max(emission_estimate) > 0.5f) ? EMISSION_SAMPLING_FRONT_BACK :
-                                                                 EMISSION_SAMPLING_NONE;
+    emission_sampling = (reduce_max(fabs(emission_estimate)) > 0.5f) ?
+                            EMISSION_SAMPLING_FRONT_BACK :
+                            EMISSION_SAMPLING_NONE;
   }
   else {
     emission_sampling = emission_sampling_method;