diff --git a/Source/build.cpp b/Source/build.cpp
index 16c4436a..32a81675 100644
--- a/Source/build.cpp
+++ b/Source/build.cpp
@@ -2141,7 +2141,7 @@ again:
 #endif // NSIS_CONFIG_VISIBLE_SUPPORT
 
 #ifdef NSIS_CONFIG_COMPONENTPAGE
-void CEXEBuild::PreperInstTypes()
+void CEXEBuild::PrepareInstTypes()
 {
   if (!(cur_header->flags & CH_FLAGS_NO_CUSTOM))
     cur_header->install_types[NSIS_MAX_INST_TYPES] = DefineInnerLangString(NLF_COMP_CUSTOM);
@@ -2176,7 +2176,7 @@ void CEXEBuild::PreperInstTypes()
 }
 #endif
 
-void CEXEBuild::PreperHeaders(IGrowBuf *hdrbuf)
+void CEXEBuild::PrepareHeaders(IGrowBuf *hdrbuf)
 {
   hdrbuf->add(cur_header,sizeof(header));
 #ifdef NSIS_CONFIG_VISIBLE_SUPPORT
@@ -2205,17 +2205,14 @@ void CEXEBuild::PreperHeaders(IGrowBuf *hdrbuf)
   memcpy(hdrbuf->get(),cur_header,sizeof(header));
 }
 
-int CEXEBuild::write_output(void)
+int CEXEBuild::check_write_output_errors() const
 {
-#ifndef NSIS_CONFIG_CRC_SUPPORT
-  build_crcchk=0;
-#endif
   if (has_called_write_output)
   {
     ERROR_MSG("Error (write_output): write_output already called, can't continue\n");
     return PS_ERROR;
   }
-  has_called_write_output++;
+
   if (!build_output_filename[0])
   {
     ERROR_MSG("Error: invalid script: never had OutFile command\n");
@@ -2252,18 +2249,33 @@ int CEXEBuild::write_output(void)
   if (cur_page)
   {
     ERROR_MSG("Error: PageEx still open at EOF, cannot proceed\n");
-    return 1;
+    return PS_ERROR;
   }
 
   // deal with functions, for both install and uninstall modes.
   if (build_cursection_isfunc)
   {
     ERROR_MSG("Error: Function still open at EOF, cannot proceed\n");
-    return 1;
+    return PS_ERROR;
   }
 
+  return PS_OK;
+}
+
+int CEXEBuild::write_output(void)
+{
+#ifndef NSIS_CONFIG_CRC_SUPPORT
+  build_crcchk=0;
+#endif
+
   int err;
 
+  err = check_write_output_errors();
+  if (err != PS_OK)
+    return err;
+
+  has_called_write_output++;
+
 #ifdef NSIS_CONFIG_PLUGIN_SUPPORT
   err = add_plugins_dir_initializer();
   if (err != PS_OK)
@@ -2293,7 +2305,7 @@ int CEXEBuild::write_output(void)
         return PS_ERROR;
 #ifdef NSIS_CONFIG_COMPONENTPAGE 
       // set sections to the first insttype
-      PreperInstTypes();
+      PrepareInstTypes();
 #endif
       set_uninstall_mode(0);
     }
@@ -2311,7 +2323,7 @@ int CEXEBuild::write_output(void)
 
 #ifdef NSIS_CONFIG_COMPONENTPAGE
   // set sections to the first insttype
-  PreperInstTypes();
+  PrepareInstTypes();
 #endif
 
 #ifdef NSIS_CONFIG_VISIBLE_SUPPORT
@@ -2494,7 +2506,7 @@ int CEXEBuild::write_output(void)
     {
       GrowBuf hdrcomp;
 
-      PreperHeaders(&hdrcomp);
+      PrepareHeaders(&hdrcomp);
 
       if (add_data((char*)hdrcomp.get(),hdrcomp.getlen(),&ihd) < 0)
         return PS_ERROR;
@@ -2818,7 +2830,7 @@ int CEXEBuild::uninstall_generate()
 
       set_uninstall_mode(1);
 
-      PreperHeaders(&udata);
+      PrepareHeaders(&udata);
 
       fh.length_of_header=udata.getlen();
       int err=add_data((char*)udata.get(),udata.getlen(),&uhd);
@@ -3113,7 +3125,7 @@ void CEXEBuild::warning_fl(const char *s, ...)
   }
 }
 
-void CEXEBuild::ERROR_MSG(const char *s, ...)
+void CEXEBuild::ERROR_MSG(const char *s, ...) const
 {
 #ifdef _WIN32
   if (display_errors || notify_hwnd)
@@ -3139,7 +3151,7 @@ void CEXEBuild::ERROR_MSG(const char *s, ...)
   }
 }
 
-void CEXEBuild::SCRIPT_MSG(const char *s, ...)
+void CEXEBuild::SCRIPT_MSG(const char *s, ...) const
 {
   if (display_script)
   {
@@ -3151,7 +3163,7 @@ void CEXEBuild::SCRIPT_MSG(const char *s, ...)
   }
 }
 
-void CEXEBuild::INFO_MSG(const char *s, ...)
+void CEXEBuild::INFO_MSG(const char *s, ...) const
 {
   if (display_info)
   {
@@ -3179,7 +3191,7 @@ void CEXEBuild::print_warnings()
 }
 
 #ifdef _WIN32
-void CEXEBuild::notify(notify_e code, char *data)
+void CEXEBuild::notify(notify_e code, char *data) const
 {
   if (notify_hwnd)
   {
diff --git a/Source/build.h b/Source/build.h
index de6debc1..b1354cb8 100644
--- a/Source/build.h
+++ b/Source/build.h
@@ -106,12 +106,14 @@ class CEXEBuild {
 
 #ifdef _WIN32
     HWND notify_hwnd;
-    void notify(notify_e code, char *data);
+    void notify(notify_e code, char *data) const;
 #else
-    void notify(notify_e code, char *data) { }
+    void notify(notify_e code, char *data) const { }
 #endif
 
   private:
+    int check_write_output_errors() const;
+
     // tokens.cpp
     int get_commandtoken(char *s, int *np, int *op, int *pos);
     int IsTokenPlacedRight(int pos, char *tok);
@@ -160,9 +162,9 @@ class CEXEBuild {
     bool inside_comment;
     int multiple_entries_instruction;
 
-    void ERROR_MSG(const char *s, ...);
-    void SCRIPT_MSG(const char *s, ...);
-    void INFO_MSG(const char *s, ...);
+    void ERROR_MSG(const char *s, ...) const;
+    void SCRIPT_MSG(const char *s, ...) const;
+    void INFO_MSG(const char *s, ...) const;
 
 #ifdef NSIS_CONFIG_PLUGIN_SUPPORT
     int add_plugins_dir_initializer(void);
@@ -205,8 +207,8 @@ class CEXEBuild {
 
     int AddVersionInfo();
     int ProcessPages();
-    void PreperInstTypes();
-    void PreperHeaders(IGrowBuf *hdrbuf);
+    void PrepareInstTypes();
+    void PrepareHeaders(IGrowBuf *hdrbuf);
 
     int resolve_jump_int(const char *fn, int *a, int offs, int start, int end);
     int resolve_call_int(const char *fn, const char *str, int fptr, int *ofs);
diff --git a/Source/strlist.h b/Source/strlist.h
index 26a58523..3a90e93b 100644
--- a/Source/strlist.h
+++ b/Source/strlist.h
@@ -11,23 +11,25 @@
 #  include <unistd.h>
 #endif
 
+#include <cassert> // for assert
+
 class IGrowBuf
 {
   public:
     virtual int add(const void *data, int len)=0;
     virtual void resize(int newlen)=0;
-    virtual int getlen()=0;
-    virtual void *get()=0;
+    virtual int getlen() const=0;
+    virtual void *get() const=0;
 };
 
 class IMMap
 {
   public:
     virtual void resize(int newlen)=0;
-    virtual int getsize()=0;
-    virtual void *get(int offset, int size)=0;
-    virtual void *get(int offset, int *size)=0;
-    virtual void *getmore(int offset, int *size)=0;
+    virtual int getsize() const=0;
+    virtual void *get(int offset, int size) const=0;
+    virtual void *get(int offset, int *size) const=0;
+    virtual void *getmore(int offset, int *size) const=0;
     virtual void release()=0;
     virtual void release(void *view, int size)=0;
     virtual void clear()=0;
@@ -97,8 +99,8 @@ class GrowBuf : public IGrowBuf
       }
     }
 
-    int getlen() { return m_used; }
-    void *get() { return m_s; }
+    int getlen() const { return m_used; }
+    void *get() const { return m_s; }
 
   private:
     void *m_s;
@@ -189,7 +191,7 @@ public:
   }
 
   char *get() { return (char*)gr.get(); }
-  int getlen() { return gr.getlen(); }
+  int getlen() const { return gr.getlen(); }
 private:
   GrowBuf gr;
 };
@@ -467,17 +469,17 @@ class FastStringList : public SortedStringListND<struct string_t>
       return ((struct string_t*)gr.get())[pos].name;
     }
 
-    char *get()
+    char *get() const
     {
       return (char*)strings.get();
     }
 
-    int getlen()
+    int getlen() const
     {
       return strings.getlen();
     }
 
-    int getnum()
+    int getnum() const
     {
       return gr.getlen()/sizeof(struct string_t);
     }
@@ -678,23 +680,22 @@ class MMapFile : public IMMap
       }
     }
 
-    int getsize()
+    int getsize() const
     {
       return m_iSize;
     }
 
-    void *get(int offset, int size)
+    void *get(int offset, int size) const
     {
       return get(offset, &size);
     }
 
-    void *get(int offset, int *sizep)
+    void *get(int offset, int *sizep) const
     {
       if (!sizep)
         return NULL;
 
-      if (m_pView)
-        release();
+      assert(!m_pView);
 
       int size = *sizep;
 
@@ -715,10 +716,12 @@ class MMapFile : public IMMap
       size += offset - alignedoffset;
 
 #ifdef _WIN32
-      m_pView = MapViewOfFile(m_hFileMap, m_bReadOnly ? FILE_MAP_READ : FILE_MAP_WRITE, 0, alignedoffset, size);
+      const_cast<MMapFile*>(this)->m_pView =
+        MapViewOfFile(m_hFileMap, m_bReadOnly ? FILE_MAP_READ : FILE_MAP_WRITE, 0, alignedoffset, size);
 #else
-      m_pView = mmap(0, size, m_bReadOnly ? PROT_READ : PROT_READ | PROT_WRITE, MAP_SHARED, m_hFileDesc, alignedoffset);
-      m_iMappedSize = *sizep = size;
+      const_cast<MMapFile*>(this)->m_pView =
+        mmap(0, size, m_bReadOnly ? PROT_READ : PROT_READ | PROT_WRITE, MAP_SHARED, m_hFileDesc, alignedoffset);
+      const_cast<MMapFile*>(this)->m_iMappedSize = *sizep = size;
 #endif
 
 #ifdef _WIN32
@@ -740,18 +743,18 @@ class MMapFile : public IMMap
       return (void *)((char *)m_pView + offset - alignedoffset);
     }
 
-    void *getmore(int offset, int *size)
+    void *getmore(int offset, int *size) const
     {
       void *pView;
       void *pViewBackup = m_pView;
 #ifndef _WIN32
       int iMappedSizeBackup = m_iMappedSize;
 #endif
-      m_pView = 0;
+      const_cast<MMapFile*>(this)->m_pView = 0;
       pView = get(offset, size);
-      m_pView = pViewBackup;
+      const_cast<MMapFile*>(this)->m_pView = pViewBackup;
 #ifndef _WIN32
-      m_iMappedSize = iMappedSizeBackup;
+      const_cast<MMapFile*>(this)->m_iMappedSize = iMappedSizeBackup;
 #endif
       return pView;
     }
@@ -822,24 +825,24 @@ class MMapFake : public IMMap
       m_iSize = iSize;
     }
 
-    int getsize()
+    int getsize() const
     {
       return m_iSize;
     }
 
-    void *get(int offset, int size)
+    void *get(int offset, int size) const
     {
       return get(offset, &size);
     }
 
-    void *get(int offset, int *size)
+    void *get(int offset, int *size) const
     {
       if (!size || (offset + *size > m_iSize))
         return NULL;
       return (void *)(m_pMem + offset);
     }
 
-    void *getmore(int offset, int *size)
+    void *getmore(int offset, int *size) const
     {
       return get(offset, size);
     }
@@ -911,26 +914,26 @@ class MMapBuf : public IGrowBuf, public IMMap
       }
     }
 
-    int getsize()
+    int getsize() const
     {
       if (m_gb_u)
         return m_fm.getsize();
       return m_gb.getlen();
     }
 
-    int getlen()
+    int getlen() const
     {
       if (m_gb_u)
         return m_used;
       return m_gb.getlen();
     }
 
-    void *get()
+    void *get() const
     {
       return get(0, m_alloc);
     }
 
-    void *get(int offset, int *sizep)
+    void *get(int offset, int *sizep) const
     {
       if (!sizep)
         return NULL;
@@ -938,14 +941,14 @@ class MMapBuf : public IGrowBuf, public IMMap
       return get(offset, size);
     }
 
-    void *get(int offset, int size)
+    void *get(int offset, int size) const
     {
       if (m_gb_u)
         return m_fm.get(offset, size);
       return (void *) ((char *) m_gb.get() + offset);
     }
 
-    void *getmore(int offset, int *size)
+    void *getmore(int offset, int *size) const
     {
       if (m_gb_u)
         return m_fm.getmore(offset, size);