diff --git a/common/mathlib.cc b/common/mathlib.cc
index d4c53d40..0d51db59 100644
--- a/common/mathlib.cc
+++ b/common/mathlib.cc
@@ -667,3 +667,14 @@ float DistToLine(const glm::vec3 &v, const glm::vec3 &w, const glm::vec3& p)
     
     return glm::distance(p, p_projected_on_vw);
 }
+
+float DistToLineSegment(const glm::vec3 &v, const glm::vec3 &w, const glm::vec3& p)
+{
+    const float frac = FractionOfLine(v, w, p);
+    if (frac > 1)
+        return glm::distance(w, p);
+    if (frac < 0)
+        return glm::distance(v, p);
+    
+    return DistToLine(v, w, p);
+}
diff --git a/include/common/mathlib.hh b/include/common/mathlib.hh
index 5bf042d5..97f105aa 100644
--- a/include/common/mathlib.hh
+++ b/include/common/mathlib.hh
@@ -296,10 +296,16 @@ glm::vec3 GLM_PolyRandomPoint(const std::vector<glm::vec3> &points);
 float FractionOfLine(const glm::vec3 &v, const glm::vec3 &w, const glm::vec3& p);
 
 /**
- * Distance from `p` to the line v<->w
+ * Distance from `p` to the line v<->w (extending infinitely in either direction)
  */
 float DistToLine(const glm::vec3 &v, const glm::vec3 &w, const glm::vec3& p);
 
+/**
+ * Distance from `p` to the line segment v<->w.
+ * i.e., 0 if `p` is between v and w.
+ */
+float DistToLineSegment(const glm::vec3 &v, const glm::vec3 &w, const glm::vec3& p);
+
 // Returns weights for f(0,0), f(1,0), f(0,1), f(1,1)
 // from: https://en.wikipedia.org/wiki/Bilinear_interpolation#Unit_Square
 static inline glm::vec4 bilinearWeights(const float x, const float y) {
diff --git a/light/test_light.cc b/light/test_light.cc
index 20b2c301..371a505c 100644
--- a/light/test_light.cc
+++ b/light/test_light.cc
@@ -542,6 +542,21 @@ TEST(mathlib, DistToLine) {
     ASSERT_TRUE(fabs(0.5 - DistToLine(vec3(10,0,0), vec3(10,0,100), vec3(9.5,0,0))) < epsilon);
 }
 
+TEST(mathlib, DistToLineSegment) {
+    const float epsilon = 0.001;
+    
+    ASSERT_TRUE(fabs(0 - DistToLineSegment(vec3(0,0,0), vec3(1,1,1), vec3(0,0,0))) < epsilon);
+    ASSERT_TRUE(fabs(0 - DistToLineSegment(vec3(0,0,0), vec3(1,1,1), vec3(0.5, 0.5, 0.5))) < epsilon);
+    ASSERT_TRUE(fabs(0 - DistToLineSegment(vec3(0,0,0), vec3(1,1,1), vec3(1,1,1))) < epsilon);
+    ASSERT_TRUE(fabs(sqrt(3) - DistToLineSegment(vec3(0,0,0), vec3(1,1,1), vec3(2,2,2))) < epsilon);
+    ASSERT_TRUE(fabs(sqrt(3) - DistToLineSegment(vec3(0,0,0), vec3(1,1,1), vec3(-1,-1,-1))) < epsilon);
+    
+    ASSERT_TRUE(fabs(sqrt(2)/2 - DistToLineSegment(vec3(0,0,0), vec3(1,1,0), vec3(0,1,0))) < epsilon);
+    ASSERT_TRUE(fabs(sqrt(2)/2 - DistToLineSegment(vec3(0,0,0), vec3(1,1,0), vec3(1,0,0))) < epsilon);
+    
+    ASSERT_TRUE(fabs(0.5 - DistToLineSegment(vec3(10,0,0), vec3(10,0,100), vec3(9.5,0,0))) < epsilon);
+}
+
 // mesh_t
 
 TEST(mathlib, meshCreate) {