diff --git a/common/bsputils.cc b/common/bsputils.cc
index c18cfbe0..f3fa9a3b 100644
--- a/common/bsputils.cc
+++ b/common/bsputils.cc
@@ -625,6 +625,57 @@ void DecompressRow(const uint8_t *in, const int numbytes, uint8_t *decompressed)
     } while (out - decompressed < row);
 }
 
+size_t DecompressedVisSize(const mbsp_t *bsp)
+{
+    if (bsp->loadversion->game->id == GAME_QUAKE_II) {
+        return (bsp->dvis.bit_offsets.size() + 7) / 8;
+    }
+
+    return (bsp->dmodels[0].visleafs + 7) / 8;
+}
+
+// from DarkPlaces
+void Mod_Q1BSP_DecompressVis(const uint8_t *in, const uint8_t *inend, uint8_t *out, uint8_t *outend)
+{
+    int c;
+    uint8_t *outstart = out;
+    while (out < outend) {
+        if (in == inend) {
+            logging::print("Mod_Q1BSP_DecompressVis: input underrun (decompressed {} of {} output bytes)\n",
+                (out - outstart), (outend - outstart));
+            return;
+        }
+
+        c = *in++;
+        if (c) {
+            *out++ = c;
+            continue;
+        }
+
+        if (in == inend) {
+            logging::print(
+                "Mod_Q1BSP_DecompressVis: input underrun (during zero-run) (decompressed {} of {} output bytes)\n",
+                (out - outstart), (outend - outstart));
+            return;
+        }
+
+        const int run_length = *in++;
+        if (!run_length) {
+            logging::print("Mod_Q1BSP_DecompressVis: 0 repeat\n");
+            return;
+        }
+
+        for (c = run_length; c > 0; c--) {
+            if (out == outend) {
+                logging::print("Mod_Q1BSP_DecompressVis: output overrun (decompressed {} of {} output bytes)\n",
+                    (out - outstart), (outend - outstart));
+                return;
+            }
+            *out++ = 0;
+        }
+    }
+}
+
 bspx_decoupled_lm_perface BSPX_DecoupledLM(const bspxentries_t &entries, int face_num)
 {
     auto &lump_bytes = entries.at("DECOUPLED_LM");
diff --git a/include/common/bsputils.hh b/include/common/bsputils.hh
index 506d0686..b104223b 100644
--- a/include/common/bsputils.hh
+++ b/include/common/bsputils.hh
@@ -107,6 +107,8 @@ void Face_DebugPrint(const mbsp_t *bsp, const mface_t *face);
 
 void CompressRow(const uint8_t *vis, const size_t numbytes, std::back_insert_iterator<std::vector<uint8_t>> it);
 void DecompressRow(const uint8_t *in, const int numbytes, uint8_t *decompressed);
+size_t DecompressedVisSize(const mbsp_t *bsp);
+void Mod_Q1BSP_DecompressVis(const uint8_t *in, const uint8_t *inend, uint8_t *out, uint8_t *outend);
 
 bspx_decoupled_lm_perface BSPX_DecoupledLM(const bspxentries_t &entries, int face_num);
 
diff --git a/light/ltface.cc b/light/ltface.cc
index 1d378d30..d957d396 100644
--- a/light/ltface.cc
+++ b/light/ltface.cc
@@ -449,57 +449,6 @@ static void CalcPoints(
     }
 }
 
-static size_t DecompressedVisSize(const mbsp_t *bsp)
-{
-    if (bsp->loadversion->game->id == GAME_QUAKE_II) {
-        return (bsp->dvis.bit_offsets.size() + 7) / 8;
-    }
-
-    return (bsp->dmodels[0].visleafs + 7) / 8;
-}
-
-// from DarkPlaces
-static void Mod_Q1BSP_DecompressVis(const uint8_t *in, const uint8_t *inend, uint8_t *out, uint8_t *outend)
-{
-    int c;
-    uint8_t *outstart = out;
-    while (out < outend) {
-        if (in == inend) {
-            logging::print("Mod_Q1BSP_DecompressVis: input underrun (decompressed {} of {} output bytes)\n",
-                (out - outstart), (outend - outstart));
-            return;
-        }
-
-        c = *in++;
-        if (c) {
-            *out++ = c;
-            continue;
-        }
-
-        if (in == inend) {
-            logging::print(
-                "Mod_Q1BSP_DecompressVis: input underrun (during zero-run) (decompressed {} of {} output bytes)\n",
-                (out - outstart), (outend - outstart));
-            return;
-        }
-
-        const int run_length = *in++;
-        if (!run_length) {
-            logging::print("Mod_Q1BSP_DecompressVis: 0 repeat\n");
-            return;
-        }
-
-        for (c = run_length; c > 0; c--) {
-            if (out == outend) {
-                logging::print("Mod_Q1BSP_DecompressVis: output overrun (decompressed {} of {} output bytes)\n",
-                    (out - outstart), (outend - outstart));
-                return;
-            }
-            *out++ = 0;
-        }
-    }
-}
-
 static bool Mod_LeafPvs(const mbsp_t *bsp, const mleaf_t *leaf, uint8_t *out)
 {
     const size_t num_pvsclusterbytes = DecompressedVisSize(bsp);
diff --git a/vis/soundpvs.cc b/vis/soundpvs.cc
index 8a790bbd..b5908322 100644
--- a/vis/soundpvs.cc
+++ b/vis/soundpvs.cc
@@ -168,6 +168,8 @@ void CalcPHS(mbsp_t *bsp)
     std::vector<uint8_t> compressed(leafbytes * 2);
     std::vector<uint8_t> uncompressed_orig(leafbytes);
 
+    std::vector<uint8_t> uncompressed_test(leafbytes);
+
     int32_t count = 0;
     for (int32_t i = 0; i < portalleafs; i++) {
         const uint8_t *scan = bsp->dvis.bits.data() + bsp->dvis.get_bit_offset(VIS_PVS, i);
@@ -175,6 +177,13 @@ void CalcPHS(mbsp_t *bsp)
         DecompressRow(scan, leafbytes, uncompressed.data());
         std::copy(uncompressed.begin(), uncompressed.end(), uncompressed_orig.begin());
 
+        // migrating to this... for now, just check it produces the same value as the legacy function
+        Mod_Q1BSP_DecompressVis(scan,
+            bsp->dvis.bits.data() + bsp->dvis.bits.size(),
+            uncompressed_test.data(),
+            uncompressed_test.data() + uncompressed_test.size());
+        Q_assert(uncompressed_test == uncompressed);
+
         scan = uncompressed_orig.data();
 
         for (int32_t j = 0; j < leafbytes; j++) {