diff --git a/src/gamedata/d_dehacked.cpp b/src/gamedata/d_dehacked.cpp
index ad62d1b61..f69ae6714 100644
--- a/src/gamedata/d_dehacked.cpp
+++ b/src/gamedata/d_dehacked.cpp
@@ -978,6 +978,17 @@ static int PatchThing (int thingy)
 			if (grp < 0) grp = -1;
 			type->ActorInfo()->projectile_group = grp;
 		}
+		else if (linelen == 12 && stricmp(Line1, "splash group") == 0)
+		{
+			stripwhite(Line2);
+			int grp = atoi(Line2);
+			if (grp < 0)
+			{
+				Printf("Splash groups must be >= 0 (check your dehacked)\n");
+				grp = 0;
+			}
+			type->ActorInfo()->splash_group = grp;
+		}
 
 		else if (linelen > 6)
 		{
diff --git a/src/playsim/p_map.cpp b/src/playsim/p_map.cpp
index 0e6e42ffe..757e8f9b1 100644
--- a/src/playsim/p_map.cpp
+++ b/src/playsim/p_map.cpp
@@ -5956,6 +5956,11 @@ int P_RadiusAttack(AActor *bombspot, AActor *bombsource, int bombdamage, int bom
 			continue;
 		}
 
+		// MBF21
+		auto targetgroup = thing->GetClass()->ActorInfo()->splash_group;
+		auto sourcegroup = bombspot->GetClass()->ActorInfo()->splash_group;
+		if (targetgroup != 0 && targetgroup == sourcegroup) continue;
+
 		// a much needed option: monsters that fire explosive projectiles cannot 
 		// be hurt by projectiles fired by a monster of the same type.
 		// Controlled by the DONTHARMCLASS and DONTHARMSPECIES flags.
diff --git a/src/scripting/thingdef_properties.cpp b/src/scripting/thingdef_properties.cpp
index 0367b8caf..64d44e669 100644
--- a/src/scripting/thingdef_properties.cpp
+++ b/src/scripting/thingdef_properties.cpp
@@ -1051,6 +1051,19 @@ DEFINE_PROPERTY(projectilegroup, I, Actor)
 	info->ActorInfo()->projectile_group = i;
 }
 
+//==========================================================================
+// MBF21
+//==========================================================================
+DEFINE_PROPERTY(splashgroup, I, Actor)
+{
+	PROP_INT_PARM(i, 0);
+	if (i < 0)
+	{
+		I_Error("Splash groups must be >= 0.");
+	}
+	info->ActorInfo()->splash_group = i;
+}
+
 //==========================================================================
 // [BB]
 //==========================================================================