diff --git a/commands2/parallelcommandgroup.py b/commands2/parallelcommandgroup.py
index 897e5ab..1a27779 100644
--- a/commands2/parallelcommandgroup.py
+++ b/commands2/parallelcommandgroup.py
@@ -49,8 +49,13 @@ def addCommands(self, *commands: Command):
         for command in commands:
             in_common = command.getRequirements().intersection(self.requirements)
             if in_common:
+                requirements_str = ", ".join(
+                    [s.getName() for s in in_common]
+                )
                 raise IllegalCommandUse(
-                    "Multiple commands in a parallel composition cannot require the same subsystems.",
+                    f"Command {command.getName()} could not be added to this ParallelCommandGroup"
+                    f" because the subsystems [{requirements_str}] are already required in this command."
+                    f" Multiple commands in a parallel composition cannot require the same subsystems.",
                     common=in_common,
                 )
 
diff --git a/commands2/paralleldeadlinegroup.py b/commands2/paralleldeadlinegroup.py
index 6a06cef..7fb4f9a 100644
--- a/commands2/paralleldeadlinegroup.py
+++ b/commands2/paralleldeadlinegroup.py
@@ -85,8 +85,13 @@ def addCommands(self, *commands: Command):
         for command in commands:
             in_common = command.getRequirements().intersection(self.requirements)
             if in_common:
+                requirements_str = ", ".join(
+                    [s.getName() for s in in_common]
+                )
                 raise IllegalCommandUse(
-                    "Multiple commands in a parallel composition cannot require the same subsystems.",
+                    f"Command {command.getName()} could not be added to this ParallelCommandGroup"
+                    f" because the subsystems [{requirements_str}] are already required in this command."
+                    f" Multiple commands in a parallel composition cannot require the same subsystems.",
                     common=in_common,
                 )
 
diff --git a/commands2/parallelracegroup.py b/commands2/parallelracegroup.py
index 032003d..04f2112 100644
--- a/commands2/parallelracegroup.py
+++ b/commands2/parallelracegroup.py
@@ -51,8 +51,13 @@ def addCommands(self, *commands: Command):
         for command in commands:
             in_common = command.getRequirements().intersection(self.requirements)
             if in_common:
+                requirements_str = ", ".join(
+                    [s.getName() for s in in_common]
+                )
                 raise IllegalCommandUse(
-                    "Multiple commands in a parallel composition cannot require the same subsystems.",
+                    f"Command {command.getName()} could not be added to this ParallelCommandGroup"
+                    f" because the subsystems [{requirements_str}] are already required in this command."
+                    f" Multiple commands in a parallel composition cannot require the same subsystems.",
                     common=in_common,
                 )