diff --git a/docs/source/release/v3.9.1/index.rst b/docs/source/release/v3.9.1/index.rst
index c61d5b619750..0a6f5567cbbc 100644
--- a/docs/source/release/v3.9.1/index.rst
+++ b/docs/source/release/v3.9.1/index.rst
@@ -25,6 +25,7 @@ Changes in this version
 -----------------------
 
 * `18833 <https://www.github.com/mantidproject/mantid/pull/18833>`_ Added check for if nonorthogonal axes should be displayed
+* `18865 <https://www.github.com/mantidproject/mantid/pull/18865>`_ Fix bug in reflectometry GUI
 * `18891 <https://www.github.com/mantidproject/mantid/pull/18891>`_ Fix bug in gd_prtn_chrg for chunked data
 * `18907 <https://www.github.com/mantidproject/mantid/pull/18907>`_ Fix zeropadding for IMAT in Facilities.XML
 * `18914 <https://www.github.com/mantidproject/mantid/pull/18914>`_ Fix mass ws deletion bug
@@ -41,6 +42,8 @@ Summary of impact
 +=======+===================================================================================+=============================================+==============+
 | 18833 | HKL axes now respect the non-orthogonal checkbox                                  | Add check if button is in a checked state   | **low**      |
 +-------+-----------------------------------------------------------------------------------+---------------------------------------------+--------------+
+| 18865 | Correct behaviour when no transmission run is provided                            | Add check if runs are provided              | **low**      |
++-------+-----------------------------------------------------------------------------------+---------------------------------------------+--------------+
 | 18891 | Fixes bug in gd_prtn_chrg for chunked data                                        | Recalculate proton charge just prior to use | **low**      |
 +-------+-----------------------------------------------------------------------------------+---------------------------------------------+--------------+
 | 18907 | Allows IMAT to use general file finding mechanism                                 | Facilities file update                      | **low**      |
diff --git a/scripts/Interface/ui/reflectometer/refl_gui.py b/scripts/Interface/ui/reflectometer/refl_gui.py
index fc808e9a7dc1..6d275c51f9a8 100644
--- a/scripts/Interface/ui/reflectometer/refl_gui.py
+++ b/scripts/Interface/ui/reflectometer/refl_gui.py
@@ -1042,7 +1042,8 @@ def _do_run(self, runno, row, which):
                     alg = AlgorithmManager.create("ReflectometryReductionOneAuto")
                     alg.initialize()
                     alg.setProperty("InputWorkspace", ws[i])
-                    alg.setProperty("FirstTransmissionRun", group_trans_ws)
+                    if group_trans_ws:
+                        alg.setProperty("FirstTransmissionRun", group_trans_ws)
                     if angle is not None:
                         alg.setProperty("ThetaIn", angle)
                     alg.setProperty("OutputWorkspaceBinned", runno+'_IvsQ_binned_'+str(i+1))
@@ -1066,7 +1067,7 @@ def _do_run(self, runno, row, which):
                     wlamGroup.append(wlam)
                     thetaGroup.append(th)
 
-                wqBinned = GroupWorkspaces(InputWorkspaces=wqGroup, OutputWorkspace=runno+'_IvsQ_binned')
+                wqBinned = GroupWorkspaces(InputWorkspaces=wqGroupBinned, OutputWorkspace=runno+'_IvsQ_binned')
                 wq = GroupWorkspaces(InputWorkspaces=wqGroup, OutputWorkspace=runno+'_IvsQ')
                 wlam = GroupWorkspaces(InputWorkspaces=wlamGroup, OutputWorkspace=runno+'_IvsLam')
                 th = thetaGroup[0]
@@ -1074,7 +1075,8 @@ def _do_run(self, runno, row, which):
                 alg = AlgorithmManager.create("ReflectometryReductionOneAuto")
                 alg.initialize()
                 alg.setProperty("InputWorkspace", ws)
-                alg.setProperty("FirstTransmissionRun", transmission_ws)
+                if transmission_ws:
+                    alg.setProperty("FirstTransmissionRun", transmission_ws)
                 if angle is not None:
                     alg.setProperty("ThetaIn", angle)
                 alg.setProperty("OutputWorkspaceBinned", runno+'_IvsQ_binned')