diff --git a/dbfopen.c b/dbfopen.c
index cc0ab06..1b8995d 100644
--- a/dbfopen.c
+++ b/dbfopen.c
@@ -366,7 +366,7 @@ static int DBFGetLenWithoutExtension(const char *pszBasename)
 /************************************************************************/
 
 DBFHandle SHPAPI_CALL DBFOpenLL(const char *pszFilename, const char *pszAccess,
-                                SAHooks *psHooks)
+                                const SAHooks *psHooks)
 {
     /* -------------------------------------------------------------------- */
     /*      We only allow the access strings "rb" and "r+".                  */
@@ -647,7 +647,8 @@ DBFHandle SHPAPI_CALL DBFCreateEx(const char *pszFilename,
 /************************************************************************/
 
 DBFHandle SHPAPI_CALL DBFCreateLL(const char *pszFilename,
-                                  const char *pszCodePage, SAHooks *psHooks)
+                                  const char *pszCodePage,
+                                  const SAHooks *psHooks)
 {
     /* -------------------------------------------------------------------- */
     /*	Compute the base (layer) name.  If there is any extension	*/
diff --git a/sbnsearch.c b/sbnsearch.c
index 90f1ea7..afc7929 100644
--- a/sbnsearch.c
+++ b/sbnsearch.c
@@ -151,7 +151,8 @@ static void SwapWord(int length, void *wordP)
 /*                         SBNOpenDiskTree()                            */
 /************************************************************************/
 
-SBNSearchHandle SBNOpenDiskTree(const char *pszSBNFilename, SAHooks *psHooks)
+SBNSearchHandle SBNOpenDiskTree(const char *pszSBNFilename,
+                                const SAHooks *psHooks)
 {
     /* -------------------------------------------------------------------- */
     /*  Establish the byte order on this machine.                           */
diff --git a/shapefil.h b/shapefil.h
index 59793f1..c941e1f 100644
--- a/shapefil.h
+++ b/shapefil.h
@@ -269,13 +269,13 @@ extern "C"
     SHPHandle SHPAPI_CALL SHPOpen(const char *pszShapeFile,
                                   const char *pszAccess);
     SHPHandle SHPAPI_CALL SHPOpenLL(const char *pszShapeFile,
-                                    const char *pszAccess, SAHooks *psHooks);
+                                    const char *pszAccess, const SAHooks *psHooks);
     SHPHandle SHPAPI_CALL SHPOpenLLEx(const char *pszShapeFile,
-                                      const char *pszAccess, SAHooks *psHooks,
+                                      const char *pszAccess, const SAHooks *psHooks,
                                       int bRestoreSHX);
 
     int SHPAPI_CALL SHPRestoreSHX(const char *pszShapeFile,
-                                  const char *pszAccess, SAHooks *psHooks);
+                                  const char *pszAccess, const SAHooks *psHooks);
 
     /* If setting bFastMode = TRUE, the content of SHPReadObject() is owned by the SHPHandle. */
     /* So you cannot have 2 valid instances of SHPReadObject() simultaneously. */
@@ -285,7 +285,7 @@ extern "C"
 
     SHPHandle SHPAPI_CALL SHPCreate(const char *pszShapeFile, int nShapeType);
     SHPHandle SHPAPI_CALL SHPCreateLL(const char *pszShapeFile, int nShapeType,
-                                      SAHooks *psHooks);
+                                      const SAHooks *psHooks);
     void SHPAPI_CALL SHPGetInfo(SHPHandle hSHP, int *pnEntities,
                                 int *pnShapeType, double *padfMinBound,
                                 double *padfMaxBound);
@@ -376,7 +376,7 @@ extern "C"
     typedef struct SHPDiskTreeInfo *SHPTreeDiskHandle;
 
     SHPTreeDiskHandle SHPAPI_CALL SHPOpenDiskTree(const char *pszQIXFilename,
-                                                  SAHooks *psHooks);
+                                                  const SAHooks *psHooks);
 
     void SHPAPI_CALL SHPCloseDiskTree(SHPTreeDiskHandle hDiskTree);
 
@@ -385,7 +385,7 @@ extern "C"
                             double *padfBoundsMax, int *pnShapeCount);
 
     int SHPAPI_CALL SHPWriteTreeLL(SHPTree *hTree, const char *pszFilename,
-                                   SAHooks *psHooks);
+                                   const SAHooks *psHooks);
 
     /* -------------------------------------------------------------------- */
     /*      SBN Search API                                                  */
@@ -394,7 +394,7 @@ extern "C"
     typedef struct SBNSearchInfo *SBNSearchHandle;
 
     SBNSearchHandle SHPAPI_CALL SBNOpenDiskTree(const char *pszSBNFilename,
-                                                SAHooks *psHooks);
+                                                const SAHooks *psHooks);
 
     void SHPAPI_CALL SBNCloseDiskTree(SBNSearchHandle hSBN);
 
@@ -483,13 +483,13 @@ extern "C"
     DBFHandle SHPAPI_CALL DBFOpen(const char *pszDBFFile,
                                   const char *pszAccess);
     DBFHandle SHPAPI_CALL DBFOpenLL(const char *pszDBFFile,
-                                    const char *pszAccess, SAHooks *psHooks);
+                                    const char *pszAccess, const SAHooks *psHooks);
     DBFHandle SHPAPI_CALL DBFCreate(const char *pszDBFFile);
     DBFHandle SHPAPI_CALL DBFCreateEx(const char *pszDBFFile,
                                       const char *pszCodePage);
     DBFHandle SHPAPI_CALL DBFCreateLL(const char *pszDBFFile,
                                       const char *pszCodePage,
-                                      SAHooks *psHooks);
+                                      const SAHooks *psHooks);
 
     int SHPAPI_CALL DBFGetFieldCount(DBFHandle psDBF);
     int SHPAPI_CALL DBFGetRecordCount(DBFHandle psDBF);
diff --git a/shpopen.c b/shpopen.c
index 681671a..eaf2911 100644
--- a/shpopen.c
+++ b/shpopen.c
@@ -311,7 +311,7 @@ static int SHPGetLenWithoutExtension(const char *pszBasename)
 /************************************************************************/
 
 SHPHandle SHPAPI_CALL SHPOpenLL(const char *pszLayer, const char *pszAccess,
-                                SAHooks *psHooks)
+                                const SAHooks *psHooks)
 {
     /* -------------------------------------------------------------------- */
     /*      Ensure the access string is one of the legal ones.  We          */
@@ -666,7 +666,7 @@ SHPHandle SHPAPI_CALL SHPOpenLL(const char *pszLayer, const char *pszAccess,
 /************************************************************************/
 
 SHPHandle SHPAPI_CALL SHPOpenLLEx(const char *pszLayer, const char *pszAccess,
-                                  SAHooks *psHooks, int bRestoreSHX)
+                                  const SAHooks *psHooks, int bRestoreSHX)
 {
     if (!bRestoreSHX)
         return SHPOpenLL(pszLayer, pszAccess, psHooks);
@@ -689,7 +689,7 @@ SHPHandle SHPAPI_CALL SHPOpenLLEx(const char *pszLayer, const char *pszAccess,
 /************************************************************************/
 
 int SHPAPI_CALL SHPRestoreSHX(const char *pszLayer, const char *pszAccess,
-                              SAHooks *psHooks)
+                              const SAHooks *psHooks)
 {
     /* -------------------------------------------------------------------- */
     /*      Ensure the access string is one of the legal ones.  We          */
@@ -981,7 +981,7 @@ SHPHandle SHPAPI_CALL SHPCreate(const char *pszLayer, int nShapeType)
 /************************************************************************/
 
 SHPHandle SHPAPI_CALL SHPCreateLL(const char *pszLayer, int nShapeType,
-                                  SAHooks *psHooks)
+                                  const SAHooks *psHooks)
 {
 /* -------------------------------------------------------------------- */
 /*      Establish the byte order on this system.                        */
diff --git a/shptree.c b/shptree.c
index 0e9c051..067ebbb 100644
--- a/shptree.c
+++ b/shptree.c
@@ -727,7 +727,8 @@ struct SHPDiskTreeInfo
 /*                         SHPOpenDiskTree()                            */
 /************************************************************************/
 
-SHPTreeDiskHandle SHPOpenDiskTree(const char *pszQIXFilename, SAHooks *psHooks)
+SHPTreeDiskHandle SHPOpenDiskTree(const char *pszQIXFilename,
+                                  const SAHooks *psHooks)
 {
     SHPTreeDiskHandle hDiskTree;
 
@@ -1049,7 +1050,8 @@ static int SHPGetSubNodeOffset(SHPTreeNode *node)
 /*                          SHPWriteTreeNode()                          */
 /************************************************************************/
 
-static void SHPWriteTreeNode(SAFile fp, SHPTreeNode *node, SAHooks *psHooks)
+static void SHPWriteTreeNode(SAFile fp, SHPTreeNode *node,
+                             const SAHooks *psHooks)
 {
     int i, j;
     int offset;
@@ -1111,7 +1113,8 @@ int SHPAPI_CALL SHPWriteTree(SHPTree *tree, const char *filename)
 /*                           SHPWriteTreeLL()                           */
 /************************************************************************/
 
-int SHPWriteTreeLL(SHPTree *tree, const char *filename, SAHooks *psHooks)
+int SHPWriteTreeLL(SHPTree *tree, const char *filename,
+                   const SAHooks *psHooks)
 {
     char signature[4] = "SQT";
     int i;