diff --git a/src/server/defs.h b/src/server/defs.h
index d0b48f3..35c5554 100644
--- a/src/server/defs.h
+++ b/src/server/defs.h
@@ -17,3 +17,19 @@
 #include "gamerules.h"
 #include "../../../valve/src/server/items.h"
 #include "../../../valve/src/server/flashlight.h"
+
+/* returns if a player already has a teleporter/exit built */
+bool
+TFC_ExistsForPlayer(entity pl, string cname)
+{
+	/* loop through all exits */
+	for (entity e = world; (e = find(e, ::classname, cname));) {
+		/* if it's not places by our owner... */
+		if (e.real_owner != pl)
+			continue;
+
+		return true;
+	}
+
+	return false;
+}
diff --git a/src/server/dispenser.qc b/src/server/dispenser.qc
index 1a1f156..d476ba7 100644
--- a/src/server/dispenser.qc
+++ b/src/server/dispenser.qc
@@ -75,6 +75,17 @@ CSEv_TFC_BuildDispenser_(void)
 		return;
 	}
 
+	/* can't build in the air */
+	if (!(pl.flags & FL_ONGROUND)) {
+		env_message_single(pl, "#Build_air");
+		return;
+	}
+
+	if (TFC_ExistsForPlayer(pl, "TFCDispenser")) {
+		env_message_single(pl, "#Build_onedispenser");
+		return;
+	}
+
 	pl.m_iAmmoCells -= TFC_DISPENSER_COST;
 
 	/* deploy */
diff --git a/src/server/sentry.qc b/src/server/sentry.qc
index 1dbc03e..2db8aa5 100644
--- a/src/server/sentry.qc
+++ b/src/server/sentry.qc
@@ -85,6 +85,17 @@ CSEv_TFC_BuildSentry_(void)
 		return;
 	}
 
+	/* can't build in the air */
+	if (!(pl.flags & FL_ONGROUND)) {
+		env_message_single(pl, "#Build_air");
+		return;
+	}
+
+	if (TFC_ExistsForPlayer(pl, "TFCSentry")) {
+		env_message_single(pl, "#Build_onesentry");
+		return;
+	}
+
 	pl.m_iAmmoCells -= TFC_SENTRY_COST;
 
 	/* deploy */
diff --git a/src/server/teleporter.qc b/src/server/teleporter.qc
index 9a642fd..1f14239 100644
--- a/src/server/teleporter.qc
+++ b/src/server/teleporter.qc
@@ -141,6 +141,17 @@ CSEv_TFC_BuildTele_(void)
 		return;
 	}
 
+	/* can't build in the air */
+	if (!(pl.flags & FL_ONGROUND)) {
+		env_message_single(pl, "#Build_air");
+		return;
+	}
+
+	if (TFC_ExistsForPlayer(pl, "TFCTeleport")) {
+		env_message_single(pl, "You can only have one teleporter.");
+		return;
+	}
+
 	pl.m_iAmmoCells -= TFC_TELEPORTER_COST;
 
 	/* deploy */
@@ -164,6 +175,17 @@ CSEv_TFC_BuildTeleExit_(void)
 		return;
 	}
 
+	/* can't build in the air */
+	if (!(pl.flags & FL_ONGROUND)) {
+		env_message_single(pl, "#Build_air");
+		return;
+	}
+
+	if (TFC_ExistsForPlayer(pl, "TFCTeleportExit")) {
+		env_message_single(pl, "You can only have one teleporter exit.");
+		return;
+	}
+
 	pl.m_iAmmoCells -= TFC_TELEPORTER_COST;
 
 	/* deploy */