diff --git a/qbsp/portals.cc b/qbsp/portals.cc
index f7f7ae87..002f6f9d 100644
--- a/qbsp/portals.cc
+++ b/qbsp/portals.cc
@@ -252,6 +252,16 @@ static void WritePortalfile(node_t *headnode, portal_state_t *state)
     if (!portalFile)
         FError("Failed to open {}: {}", options.szBSPName, strerror(errno));
 
+    // q2 uses a PRT1 file, but with clusters.
+    // (Since q2bsp natively supports clusters, we don't need PRT2.)
+    if (options.target_game->id == GAME_QUAKE_II) {
+        fmt::print(portalFile, "PRT1\n");
+        fmt::print(portalFile, "{}\n", state->num_visclusters);
+        fmt::print(portalFile, "{}\n", state->num_visportals);
+        WritePortals_r(headnode, portalFile, true);
+        return;
+    }
+
     /* If no detail clusters, just use a normal PRT1 format */
     if (!state->uses_detail) {
         fmt::print(portalFile, "PRT1\n");
diff --git a/vis/vis.cc b/vis/vis.cc
index e8a14592..994a3e3e 100644
--- a/vis/vis.cc
+++ b/vis/vis.cc
@@ -16,8 +16,8 @@
  */
 int numportals;
 int portalleafs; /* leafs (PRT1) or clusters (PRT2) */
-int portalleafs_real; /* real no. of leafs after expanding PRT2 clusters */
-int *clustermap; /* mapping from real leaf to cluster number */
+int portalleafs_real; /* real no. of leafs after expanding PRT2 clusters. Not used for Q2. */
+int *clustermap; /* mapping from real leaf to cluster number. Not used for Q2. */
 
 portal_t *portals;
 leaf_t *leafs;
@@ -39,7 +39,7 @@ uint8_t *uncompressed_q2; // [leafbytes*portalleafs]
 
 int leafbytes; // (portalleafs+63)>>3
 int leaflongs;
-int leafbytes_real; // (portalleafs_real+63)>>3
+int leafbytes_real; // (portalleafs_real+63)>>3, not used for Q2.
 
 /* Options - TODO: collect these in a struct */
 bool fastvis;
@@ -659,11 +659,16 @@ static void ClusterFlow(int clusternum, leafbits_t *buffer, const mbsp_t *bsp)
      * increment totalvis by
      * (# of real leafs in this cluster) x (# of real leafs visible from this cluster)
      */
+    if (bsp->loadversion->game->id == GAME_QUAKE_II) {
+        // FIXME: not sure what this is supposed to be?
+        totalvis += numvis;
+    } else {
     for (i = 0; i < portalleafs_real; i++) {
         if (clustermap[i] == clusternum) {
             totalvis += numvis;
         }
     }
+    }
 
     /* Allocate for worst case where RLE might grow the data (unlikely) */
     if (bsp->loadversion->game->id == GAME_QUAKE_II) {
@@ -684,9 +689,9 @@ static void ClusterFlow(int clusternum, leafbits_t *buffer, const mbsp_t *bsp)
     leaf->visofs = dest - vismap;
 
     // Set pointers
-    for (i = 0; i < portalleafs_real; i++) {
-        if (bsp->dleafs[i + 1].cluster == clusternum) {
-            bsp->dleafs[i + 1].visofs = leaf->visofs;
+    for (i = 1; i < bsp->numleafs; i++) {
+        if (bsp->dleafs[i].cluster == clusternum) {
+            bsp->dleafs[i].visofs = leaf->visofs;
         }
     }
 
@@ -753,7 +758,10 @@ void CalcVis(const mbsp_t *bsp)
     //
     // assemble the leaf vis lists by oring and compressing the portal lists
     //
-    if (portalleafs == portalleafs_real) {
+    if (portalleafs == portalleafs_real && bsp->loadversion->game->id != GAME_QUAKE_II) {
+        // Legacy, non-detail Q1 vis codepath
+        // FIXME: Should be possible to remove this and just use ClusterFlow even on Q1 maps
+        // with no detail.
         for (i = 0; i < portalleafs; i++)
             LeafFlow(i, &bsp->dleafs[i + 1], bsp);
     } else {
@@ -768,9 +776,15 @@ void CalcVis(const mbsp_t *bsp)
 
     int64_t avg = totalvis;
 
-    avg /= static_cast<int64_t>(portalleafs_real);
+    if (bsp->loadversion->game->id == GAME_QUAKE_II) {
+        avg /= static_cast<int64_t>(portalleafs);
 
-    LogPrint("average leafs visible: {}\n", avg);
+        LogPrint("average clusters visible: {}\n", avg);
+    } else {
+	    avg /= static_cast<int64_t>(portalleafs_real);
+
+	    LogPrint("average leafs visible: {}\n", avg);
+	}
 }
 
 /*
@@ -1023,8 +1037,8 @@ static void LoadPortals(const std::filesystem::path &name, mbsp_t *bsp)
             FError("unable to parse {} HEADER\n", PORTALFILE);
 
         if (bsp->loadversion->game->id == GAME_QUAKE_II) {
-            portalleafs_real = bsp->numleafs;
-            LogPrint("{:6} leafs\n", portalleafs_real);
+            // since q2bsp has native cluster support, we shouldn't look at portalleafs_real at all.
+            portalleafs_real = 0;
             LogPrint("{:6} clusters\n", portalleafs);
             LogPrint("{:6} portals\n", numportals);
         } else {
@@ -1036,6 +1050,9 @@ static void LoadPortals(const std::filesystem::path &name, mbsp_t *bsp)
         count = fscanf(f.get(), "%i\n%i\n%i\n", &portalleafs_real, &portalleafs, &numportals);
         if (count != 3)
             FError("unable to parse {} HEADER\n", PORTALFILE);
+        if (bsp->loadversion->game->id == GAME_QUAKE_II) {
+            FError("%s can not be used with Q2\n", PORTALFILE2);
+        }
         LogPrint("{:6} leafs\n", portalleafs_real);
         LogPrint("{:6} clusters\n", portalleafs);
         LogPrint("{:6} portals\n", numportals);
@@ -1043,6 +1060,9 @@ static void LoadPortals(const std::filesystem::path &name, mbsp_t *bsp)
         count = fscanf(f.get(), "%i\n%i\n%i\n", &portalleafs, &numportals, &portalleafs_real);
         if (count != 3)
             FError("unable to parse {} HEADER\n", PORTALFILE);
+        if (bsp->loadversion->game->id == GAME_QUAKE_II) {
+            Error("%s: %s can not be used with Q2\n", __func__, PORTALFILEAM);
+        }
         LogPrint("{:6} leafs\n", portalleafs_real);
         LogPrint("{:6} clusters\n", portalleafs);
         LogPrint("{:6} portals\n", numportals);
@@ -1052,7 +1072,12 @@ static void LoadPortals(const std::filesystem::path &name, mbsp_t *bsp)
 
     leafbytes = ((portalleafs + 63) & ~63) >> 3;
     leaflongs = leafbytes / sizeof(long);
+    if (bsp->loadversion->game->id == GAME_QUAKE_II) {
+        // not used in Q2
+        leafbytes_real = 0;
+    } else {
     leafbytes_real = ((portalleafs_real + 63) & ~63) >> 3;
+    }
 
     // each file portal is split into two memory portals
     portals = new portal_t[numportals * 2] { };
@@ -1129,13 +1154,10 @@ static void LoadPortals(const std::filesystem::path &name, mbsp_t *bsp)
     }
 
     /* Load the cluster expansion map if needed */
-    /*if (bsp->loadversion->game->id == GAME_QUAKE_II) {
-        clustermap = new int[bsp->numleafs];
-
-        for (int32_t i = 0; i < bsp->numleafs; i++) {
-            clustermap[i] = bsp->dleafs[i + 1].cluster;
-        }
-    } else */if (portalleafs != portalleafs_real) {
+    if (bsp->loadversion->game->id == GAME_QUAKE_II) {
+        // not used
+        clustermap = nullptr;
+    } else if (portalleafs != portalleafs_real) {
         clustermap = new int[portalleafs_real];
         if (!strcmp(magic, PORTALFILE2)) {
             for (i = 0; i < portalleafs; i++) {