diff --git a/Source/Plugins.cpp b/Source/Plugins.cpp
index 32a664a4..64c250a0 100644
--- a/Source/Plugins.cpp
+++ b/Source/Plugins.cpp
@@ -51,8 +51,9 @@ bool contains(const C& cntnr, const K& key)
 template <class C, class K>
 const typename C::const_iterator get_iterator(const C& cntnr, const K& key)
 {
-  assert( contains(cntnr, key) );
-  return cntnr.find(key);
+  const typename C::const_iterator it = cntnr.find(key);
+  assert(cntnr.end() != it);
+  return it;
 }
 
 template <class C, class K> 
@@ -245,6 +246,16 @@ bool Plugins::IsPluginCommand(const tstring& token) const
   return contains(m_commands, token);
 }
 
+bool Plugins::IsKnownPlugin(const tstring& token) const
+{
+  const tstring dllname = GetDllName(token);
+  return contains(m_dllname_to_path, dllname);
+}
 
+bool Plugins::IsPluginCallSyntax(const tstring& token)
+{
+  const tstring dllname = GetDllName(token);
+  return dllname.length() + 2 < token.length();
+}
 
 #endif
diff --git a/Source/Plugins.h b/Source/Plugins.h
index cdccfb53..b7f383dc 100644
--- a/Source/Plugins.h
+++ b/Source/Plugins.h
@@ -51,9 +51,11 @@ class Plugins
     bool Initialize(const TCHAR*arcsubdir, bool displayInfo);
     void AddPluginsDir(const tstring& path, bool displayInfo);
     bool IsPluginCommand(const tstring& command) const;
+    bool IsKnownPlugin(const tstring& token) const;
     bool GetCommandInfo(const tstring&command, tstring&canoniccmd, tstring&dllPath);
     int GetDllDataHandle(bool uninst, const tstring& command) const;
     void SetDllDataHandle(bool uninst, tstring&canoniccmd, int dataHandle);
+    static bool IsPluginCallSyntax(const tstring& token);
 
   private: // methods
     void GetExports(const tstring &pathToDll, bool displayInfo);
diff --git a/Source/build.h b/Source/build.h
index 689727e6..b03945d9 100644
--- a/Source/build.h
+++ b/Source/build.h
@@ -177,7 +177,7 @@ class CEXEBuild {
     bool is_ppbranch_token(TCHAR *s);
     bool is_pp_token(int tkid);
     bool is_unsafe_pp_token(int tkid);
-    int get_commandtoken(TCHAR *s, int *np, int *op, int *pos);
+    int get_commandtoken(const TCHAR *s, int *np, int *op, int *pos);
     const TCHAR* get_commandtoken_name(int tok);
 
     /**
@@ -186,7 +186,7 @@ class CEXEBuild {
      * @return TP_FUNC, TP_SEC, TP_PAGEEX, TP_GLOBAL.
      */
     int GetCurrentTokenPlace();
-    int IsTokenPlacedRight(int pos, TCHAR *tok);
+    int IsTokenPlacedRight(int pos, const TCHAR *tok);
 
     // script.cpp
 #ifdef NSIS_SUPPORT_STANDARD_PREDEFINES
diff --git a/Source/script.cpp b/Source/script.cpp
index 061eb3fd..9daabf16 100644
--- a/Source/script.cpp
+++ b/Source/script.cpp
@@ -385,23 +385,24 @@ int CEXEBuild::doParse(const TCHAR *str)
 parse_again:
   if (line.getnumtokens() < 1) return PS_OK;
 
+  const TCHAR* const tokstr0 = line.gettoken_str(0);
   int np,op,pos;
-  int tkid=get_commandtoken(line.gettoken_str(0),&np,&op,&pos);
+  int tkid=get_commandtoken(tokstr0,&np,&op,&pos);
   if (tkid == -1)
   {
-    TCHAR *p=line.gettoken_str(0);
+    const TCHAR *p=tokstr0;
     if (p[0] && p[_tcslen(p)-1]==_T(':'))
     {
       if (p[0] == _T('!') || (p[0] >= _T('0') && p[0] <= _T('9')) || p[0] == _T('$') || p[0] == _T('-') || p[0] == _T('+'))
       {
-        ERROR_MSG(_T("Invalid label: %") NPRIs _T(" (labels cannot begin with !, $, -, +, or 0-9)\n"),line.gettoken_str(0));
+        ERROR_MSG(_T("Invalid label: %") NPRIs _T(" (labels cannot begin with !, $, -, +, or 0-9)\n"),tokstr0);
         return PS_ERROR;
       }
       extern FILE *g_output;
       if (preprocessonly)
-        _ftprintf(g_output,_T("%") NPRIs _T("\n"),line.gettoken_str(0));
+        _ftprintf(g_output,_T("%") NPRIs _T("\n"),tokstr0);
       else
-        if (add_label(line.gettoken_str(0))) return PS_ERROR;
+        if (add_label(tokstr0)) return PS_ERROR;
       line.eattoken();
       goto parse_again;
     }
@@ -411,7 +412,7 @@ parse_again:
     // We didn't recognise this command, could it be the name of a
     // function exported from a dll?
     // Plugins cannot be called in global scope so there is no need to initialize the list first
-    if (m_pPlugins && m_pPlugins->IsPluginCommand(line.gettoken_str(0)))
+    if (m_pPlugins && m_pPlugins->IsPluginCommand(tokstr0))
     {
       np   = 0;   // parameters are optional
       op   = -1;  // unlimited number of optional parameters
@@ -421,18 +422,23 @@ parse_again:
     else
 #endif
     {
-      ERROR_MSG(_T("Invalid command: %") NPRIs _T("\n"),line.gettoken_str(0));
+#ifdef NSIS_CONFIG_PLUGIN_SUPPORT
+      if (Plugins::IsPluginCallSyntax(tokstr0) && (!m_pPlugins || !m_pPlugins->IsKnownPlugin(tokstr0)))
+        ERROR_MSG(_T("Plugin not found, cannot call %") NPRIs _T("\n"),tokstr0);
+      else
+#endif
+        ERROR_MSG(_T("Invalid command: %") NPRIs _T("\n"),tokstr0);
       return PS_ERROR;
     }
   }
 
-  if (IsTokenPlacedRight(pos, line.gettoken_str(0)) != PS_OK)
+  if (IsTokenPlacedRight(pos, tokstr0) != PS_OK)
     return PS_ERROR;
 
   int v=line.getnumtokens()-(np+1);
   if (v < 0 || (op >= 0 && v > op)) // opt_parms is -1 for unlimited
   {
-    ERROR_MSG(_T("%") NPRIs _T(" expects %d"),line.gettoken_str(0),np);
+    ERROR_MSG(_T("%") NPRIs _T(" expects %d"),tokstr0,np);
     if (op < 0) ERROR_MSG(_T("+"));
     if (op > 0) ERROR_MSG(_T("-%d"),op+np);
     ERROR_MSG(_T(" parameters, got %d.\n"),line.getnumtokens()-1);
diff --git a/Source/tokens.cpp b/Source/tokens.cpp
index 9dfc7eba..75c0a185 100644
--- a/Source/tokens.cpp
+++ b/Source/tokens.cpp
@@ -360,7 +360,7 @@ bool CEXEBuild::is_unsafe_pp_token(int tkid)
   return false;
 }
 
-int CEXEBuild::get_commandtoken(TCHAR *s, int *np, int *op, int *pos)
+int CEXEBuild::get_commandtoken(const TCHAR *s, int *np, int *op, int *pos)
 {
   for (int x = 0; x < TOK__LAST; x ++)
     if (!_tcsicmp(tokenlist[x].name,s)) 
@@ -384,7 +384,7 @@ int CEXEBuild::GetCurrentTokenPlace()
   return TP_GLOBAL;
 }
 
-int CEXEBuild::IsTokenPlacedRight(int pos, TCHAR *tok)
+int CEXEBuild::IsTokenPlacedRight(int pos, const TCHAR *tok)
 {
   if (preprocessonly)
     return PS_OK;