diff --git a/src/citeme.cpp b/src/citeme.cpp
index 35ff062874..85f7f478a6 100644
--- a/src/citeme.cpp
+++ b/src/citeme.cpp
@@ -101,7 +101,7 @@ void CiteMe::add(const std::string &reference)
     if (logfile_flag == VERBOSE) logbuffer += "\n";
   }
 
-  std::size_t found = reference.find_first_of("\n");
+  std::size_t found = reference.find_first_of('\n');
   std::string header = reference.substr(0,found+1);
   if (screen_flag == VERBOSE) scrbuffer += "- " + reference;
   if (screen_flag == TERSE) scrbuffer += "- " + header;
diff --git a/src/input.cpp b/src/input.cpp
index 50e0d45aa0..97757fd1f6 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -1257,7 +1257,7 @@ void Input::shell()
 #else
       if (arg[i]) {
         std::string vardef(arg[i]);
-        auto found = vardef.find_first_of("=");
+        auto found = vardef.find_first_of('=');
         if (found == std::string::npos) {
           rv = setenv(vardef.c_str(),"",1);
         } else {
diff --git a/src/universe.cpp b/src/universe.cpp
index fc3e79ab83..005a91fc6b 100644
--- a/src/universe.cpp
+++ b/src/universe.cpp
@@ -174,7 +174,7 @@ void Universe::add_world(char *str)
     if (part.find_first_not_of("0123456789x") != std::string::npos) valid = false;
 
     if (valid) {
-      std::size_t found = part.find_first_of("x");
+      std::size_t found = part.find_first_of('x');
 
       // 'x' may not be the first or last character
 
diff --git a/src/utils.cpp b/src/utils.cpp
index 654e1a5c70..7262cf8afd 100644
--- a/src/utils.cpp
+++ b/src/utils.cpp
@@ -502,7 +502,7 @@ void utils::bounds(const char *file, int line, const std::string &str,
     return;
   }
 
-  found = str.find_first_of("*");
+  found = str.find_first_of('*');
   if (found == std::string::npos) {    // contains no '*'
     nlo = nhi = strtol(str.c_str(), nullptr, 10);
   } else if (str.size() == 1) {    // is only '*'
@@ -727,7 +727,7 @@ std::string utils::trim(const std::string &line)
 
 std::string utils::trim_comment(const std::string &line)
 {
-  auto end = line.find_first_of("#");
+  auto end = line.find_first_of('#');
   if (end != std::string::npos) { return line.substr(0, end); }
   return std::string(line);
 }
@@ -1030,7 +1030,7 @@ std::string utils::path_basename(const std::string &path)
 #if defined(_WIN32)
   size_t start = path.find_last_of("/\\");
 #else
-  size_t start = path.find_last_of("/");
+  size_t start = path.find_last_of('/');
 #endif
 
   if (start == std::string::npos) {
@@ -1051,7 +1051,7 @@ std::string utils::path_dirname(const std::string &path)
 #if defined(_WIN32)
   size_t start = path.find_last_of("/\\");
 #else
-  size_t start = path.find_last_of("/");
+  size_t start = path.find_last_of('/');
 #endif
 
   if (start == std::string::npos) return ".";