diff --git a/src/pbrt/bxdfs.cpp b/src/pbrt/bxdfs.cpp
index cd65f3c19a809af52a525535f4da7321703fe0d9..9ab74a2b077592d0c6bc003749d6d02bbec0a3f2 100644
--- a/src/pbrt/bxdfs.cpp
+++ b/src/pbrt/bxdfs.cpp
@@ -424,6 +424,9 @@ pstd::optional<BSDFSample> HairBxDF::Sample_f(Vector3f wo, Float uc, Point2f u,
         cosThetap_o = cosTheta_o;
     }
 
+    // Handle out-of-range $\cos \thetao$ from scale adjustment
+    cosThetap_o = std::abs(cosThetap_o);
+
     // Sample $M_p$ to compute $\thetai$
     Float cosTheta = 1 + v[p] * std::log(std::max<Float>(u[0], 1e-5) +
                                          (1 - u[0]) * FastExp(-2 / v[p]));
@@ -473,6 +476,9 @@ pstd::optional<BSDFSample> HairBxDF::Sample_f(Vector3f wo, Float uc, Point2f u,
         // Handle out-of-range $\cos \thetao$ from scale adjustment
         cosThetap_o = std::abs(cosThetap_o);
 
+        // Handle out-of-range $\cos \thetao$ from scale adjustment
+        cosThetap_o = std::abs(cosThetap_o);
+
         pdf += Mp(cosTheta_i, cosThetap_o, sinTheta_i, sinThetap_o, v[p]) * apPDF[p] *
                Np(dphi, p, s, gamma_o, gamma_t);
     }