diff --git a/ats/atsMachines/fluxScheduled.py b/ats/atsMachines/fluxScheduled.py
index a1492c9..18754fe 100755
--- a/ats/atsMachines/fluxScheduled.py
+++ b/ats/atsMachines/fluxScheduled.py
@@ -104,8 +104,16 @@ def init(self):
             log(("DEBUG: FluxScheduled init : self.numNodesAvailable     =%i" % (self.numNodesAvailable)), echo=True)
             log(("DEBUG: FluxScheduled init : self.numGPUsAvailable      =%i" % (self.numGPUs)), echo=True)
 
-        # Call get_physical_node to cache the hardware node listing before starting jobs
-        self.get_physical_node(0)
+        # Call get_physical_node to cache the hardware node listing before starting jobs.
+        # This is required for the same_node functionality.
+        try:
+            self.get_physical_node(0)
+        except RuntimeError:
+            # If you are not in an allocation, an exception will be thrown.
+            # We ignore the exception here and allow _cached_nodes to be None.
+            # If you are not using same_node, this is fine.  If you are using same_node,
+            # it should throw an exception when setting up the command list.
+            pass
 
     def expand_nodelist(self, nodelist_field):
         """
@@ -145,7 +153,7 @@ def get_physical_node(self, rel_index):
                         nodelist_field = parts[-1]
                         break
             if nodelist_field is None:
-                raise RuntimeError("Could not find NODELIST field in flux resource list output.")
+                raise RuntimeError("Could not find NODELIST field in flux resource list output. Use of ATS same_node feature requires running ATS within an allocation.")
             FluxScheduled._cached_nodes = self.expand_nodelist(nodelist_field)
             log(("Info: Physical Hardware Nodes: %s" % FluxScheduled._cached_nodes), echo=True)
 
diff --git a/ats/atsMachines/slurmProcessorScheduled.py b/ats/atsMachines/slurmProcessorScheduled.py
index 7eceec5..dca3b8e 100644
--- a/ats/atsMachines/slurmProcessorScheduled.py
+++ b/ats/atsMachines/slurmProcessorScheduled.py
@@ -77,8 +77,16 @@ def init(self):
 
         super(SlurmProcessorScheduled, self).init()
 
-        # Call get_physical_node to cache the hardware node listing before starting jobs
-        self.get_physical_node(0)
+        # Call get_physical_node to cache the hardware node listing before starting jobs.
+        # This is required for the same_node functionality.
+        try:
+            self.get_physical_node(0)
+        except RuntimeError:
+            # If you are not in an allocation, an exception will be thrown.
+            # We ignore the exception here and allow _cached_nodes to be None.
+            # If you are not using same_node, this is fine.  If you are using same_node,
+            # it should throw an exception when setting up the command list.
+            pass
 
     def expand_nodelist(self, nodelist_field):
         """
@@ -112,7 +120,7 @@ def get_physical_node(self, rel_index):
             nodelist_str = os.environ.get("SLURM_JOB_NODELIST")
             if not nodelist_str:
                 raise RuntimeError(
-                    "SLURM_JOB_NODELIST is not set. Are you running inside a Slurm allocation/job?"
+                    "SLURM_JOB_NODELIST is not set. Use of ATS same_node feature requires running ATS within an allocation."
                 )
 
             # Option 1: if your expand_nodelist already handles Slurm-style nodelists,