diff --git a/game.cpp b/game.cpp
index 2f5ecdc2..eddb812f 100644
--- a/game.cpp
+++ b/game.cpp
@@ -3892,7 +3892,7 @@ int pickDownDirection(cell *c, flagtype mf) {
   }
 
 template<class T> 
-cell *determinePush(cellwalker who, cell *c2, int subdir, T valid) {
+cell *determinePush(cellwalker who, cell *c2, int subdir, const T& valid) {
   if(subdir != 1 && subdir != -1) {
     subdir = 1;
     static bool first = true;
diff --git a/rogueviz-banachtarski.cpp b/rogueviz-banachtarski.cpp
index ecbc9a5c..43d098be 100644
--- a/rogueviz-banachtarski.cpp
+++ b/rogueviz-banachtarski.cpp
@@ -48,7 +48,7 @@ bool test_uniq(cellwalker cw, int z, int lev, cell *par) {
   return true;
   }
 
-template<class T> void recursively(cell *c, cell *c1, T t) {
+template<class T> void recursively(cell *c, cell *c1, const T& t) {
   t(c);
   for(int i=0; i<c->type; i++) 
     if(c->mov[i] && c->spin(i) == 0 && c->mov[i] != c1)
diff --git a/rogueviz.cpp b/rogueviz.cpp
index 5ecb97a7..a1ad2ced 100644
--- a/rogueviz.cpp
+++ b/rogueviz.cpp
@@ -1619,7 +1619,7 @@ string cname() {
   return "coord-67.txt";
   }
 
-template<class T> function<void(presmode)> roguevizslide(char c, T t) {
+template<class T> function<void(presmode)> roguevizslide(char c, const T& t) {
   return [c,t] (presmode mode) {
     patterns::canvasback = 0x101010;
     setCanvas(mode, c);
@@ -1638,7 +1638,8 @@ template<class T> function<void(presmode)> roguevizslide(char c, T t) {
     };
   }
 
-template<class T, class T1> function<void(presmode)> roguevizslide_action(char c, T t, T1 act) {
+template<class T, class U>
+function<void(presmode)> roguevizslide_action(char c, const T& t, const U& act) {
   return [c,t,act] (presmode mode) {
     patterns::canvasback = 0x101010;
     setCanvas(mode, c);