diff --git a/compiler/characterizer/stimuli.py b/compiler/characterizer/stimuli.py
index 70152a54..11dc449a 100644
--- a/compiler/characterizer/stimuli.py
+++ b/compiler/characterizer/stimuli.py
@@ -302,10 +302,12 @@ class stimuli():
                                                          OPTS.openram_temp)
             valid_retcode=0
         else:
-            # ngspice 27+ supports threading with "set num_threads=4" in the stimulus file or a .spiceinit 
-            cmd = "{0} -b -r {2}timing.raw -o {2}timing.lis {1}".format(OPTS.spice_exe,
-                                                                        temp_stim,
-                                                                        OPTS.openram_temp)
+            # ngspice 27+ supports threading with "set num_threads=4" in the stimulus file or a .spiceinit
+            # Measurements can't be made with a raw file set in ngspice
+            # -r {2}timing.raw
+            cmd = "{0} -b -o {2}timing.lis {1}".format(OPTS.spice_exe,
+                                                       temp_stim,
+                                                       OPTS.openram_temp)
             # for some reason, ngspice-25 returns 1 when it only has acceptable warnings
             valid_retcode=1