diff --git a/Source/cmFindLibraryCommand.cxx b/Source/cmFindLibraryCommand.cxx
index e7cfbebb9..6f0b23af7 100644
--- a/Source/cmFindLibraryCommand.cxx
+++ b/Source/cmFindLibraryCommand.cxx
@@ -186,7 +186,7 @@ std::string cmFindLibraryCommand::FindLibrary(const char* name)
       i != this->SearchPaths.end(); ++i)
     {
     std::string& p = *i;
-    if(p[p.size()-1] != '/')
+    if(p.empty() || p[p.size()-1] != '/')
       {
       p += "/";
       }
diff --git a/Source/cmFindPathCommand.cxx b/Source/cmFindPathCommand.cxx
index 53531dde3..628018772 100644
--- a/Source/cmFindPathCommand.cxx
+++ b/Source/cmFindPathCommand.cxx
@@ -106,7 +106,7 @@ bool cmFindPathCommand::InitialPass(std::vector<std::string> const& argsIn)
       i != this->SearchPaths.end(); ++i)
     {
     std::string& p = *i;
-    if(p[p.size()-1] != '/')
+    if(p.empty() || p[p.size()-1] != '/')
       {
       p += "/";
       }
diff --git a/Source/kwsys/SystemTools.cxx b/Source/kwsys/SystemTools.cxx
index de0001971..d20968205 100644
--- a/Source/kwsys/SystemTools.cxx
+++ b/Source/kwsys/SystemTools.cxx
@@ -2117,7 +2117,7 @@ kwsys_stl::string SystemTools
       i != path.end(); ++i)
     {
     kwsys_stl::string& p = *i;
-    if(p[p.size()-1] != '/')
+    if(p.empty() || p[p.size()-1] != '/')
       {
       p += "/";
       }
@@ -2249,7 +2249,7 @@ kwsys_stl::string SystemTools::FindProgram(
       i != path.end(); ++i)
     {
     kwsys_stl::string& p = *i;
-    if(p[p.size()-1] != '/')
+    if(p.empty() || p[p.size()-1] != '/')
       {
       p += "/";
       }
@@ -2341,7 +2341,7 @@ kwsys_stl::string SystemTools
       i != path.end(); ++i)
     {
     kwsys_stl::string& p = *i;
-    if(p[p.size()-1] != '/')
+    if(p.empty() || p[p.size()-1] != '/')
       {
       p += "/";
       }