diff --git a/jcext.c b/jcext.c
index 9c95f198..a23a957e 100644
--- a/jcext.c
+++ b/jcext.c
@@ -16,7 +16,7 @@
 
 
 GLOBAL(boolean)
-jpeg_c_bool_param_supported (j_compress_ptr cinfo, J_BOOLEAN_PARAM param)
+jpeg_c_bool_param_supported (const j_compress_ptr cinfo, J_BOOLEAN_PARAM param)
 {
   switch (param) {
   case JBOOLEAN_OPTIMIZE_SCANS:
@@ -70,7 +70,7 @@ jpeg_c_set_bool_param (j_compress_ptr cinfo, J_BOOLEAN_PARAM param,
 
 
 GLOBAL(boolean)
-jpeg_c_get_bool_param (j_compress_ptr cinfo, J_BOOLEAN_PARAM param)
+jpeg_c_get_bool_param (const j_compress_ptr cinfo, J_BOOLEAN_PARAM param)
 {
   switch(param) {
   case JBOOLEAN_OPTIMIZE_SCANS:
@@ -98,7 +98,7 @@ jpeg_c_get_bool_param (j_compress_ptr cinfo, J_BOOLEAN_PARAM param)
 
 
 GLOBAL(boolean)
-jpeg_c_float_param_supported (j_compress_ptr cinfo, J_FLOAT_PARAM param)
+jpeg_c_float_param_supported (const j_compress_ptr cinfo, J_FLOAT_PARAM param)
 {
   switch (param) {
   case JFLOAT_LAMBDA_LOG_SCALE1:
@@ -131,7 +131,7 @@ jpeg_c_set_float_param (j_compress_ptr cinfo, J_FLOAT_PARAM param, float value)
 
 
 GLOBAL(float)
-jpeg_c_get_float_param (j_compress_ptr cinfo, J_FLOAT_PARAM param)
+jpeg_c_get_float_param (const j_compress_ptr cinfo, J_FLOAT_PARAM param)
 {
   switch (param) {
   case JFLOAT_LAMBDA_LOG_SCALE1:
@@ -149,7 +149,7 @@ jpeg_c_get_float_param (j_compress_ptr cinfo, J_FLOAT_PARAM param)
 
 
 GLOBAL(boolean)
-jpeg_c_int_param_supported (j_compress_ptr cinfo, J_INT_PARAM param)
+jpeg_c_int_param_supported (const j_compress_ptr cinfo, J_INT_PARAM param)
 {
   switch (param) {
   case JINT_COMPRESS_PROFILE:
@@ -198,7 +198,7 @@ jpeg_c_set_int_param (j_compress_ptr cinfo, J_INT_PARAM param, int value)
 
 
 GLOBAL(int)
-jpeg_c_get_int_param (j_compress_ptr cinfo, J_INT_PARAM param)
+jpeg_c_get_int_param (const j_compress_ptr cinfo, J_INT_PARAM param)
 {
   switch (param) {
   case JINT_COMPRESS_PROFILE:
diff --git a/jctrans.c b/jctrans.c
index f4be9f3b..c0907849 100644
--- a/jctrans.c
+++ b/jctrans.c
@@ -69,7 +69,7 @@ jpeg_write_coefficients (j_compress_ptr cinfo, jvirt_barray_ptr * coef_arrays)
  */
 
 GLOBAL(void)
-jpeg_copy_critical_parameters (j_decompress_ptr srcinfo,
+jpeg_copy_critical_parameters (const j_decompress_ptr srcinfo,
                                j_compress_ptr dstinfo)
 {
   JQUANT_TBL ** qtblptr;
diff --git a/jdapimin.c b/jdapimin.c
index fc8898f8..e1327077 100644
--- a/jdapimin.c
+++ b/jdapimin.c
@@ -333,7 +333,7 @@ jpeg_consume_input (j_decompress_ptr cinfo)
  */
 
 GLOBAL(boolean)
-jpeg_input_complete (j_decompress_ptr cinfo)
+jpeg_input_complete (const j_decompress_ptr cinfo)
 {
   /* Check for valid jpeg object */
   if (cinfo->global_state < DSTATE_START ||
@@ -348,7 +348,7 @@ jpeg_input_complete (j_decompress_ptr cinfo)
  */
 
 GLOBAL(boolean)
-jpeg_has_multiple_scans (j_decompress_ptr cinfo)
+jpeg_has_multiple_scans (const j_decompress_ptr cinfo)
 {
   /* Only valid after jpeg_read_header completes */
   if (cinfo->global_state < DSTATE_READY ||
diff --git a/jdatasrc.c b/jdatasrc.c
index bf70422b..22a09c87 100644
--- a/jdatasrc.c
+++ b/jdatasrc.c
@@ -254,7 +254,7 @@ jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
 
 GLOBAL(void)
 jpeg_mem_src (j_decompress_ptr cinfo,
-              unsigned char * inbuffer, unsigned long insize)
+              const unsigned char * inbuffer, unsigned long insize)
 {
   struct jpeg_source_mgr * src;
 
@@ -278,6 +278,6 @@ jpeg_mem_src (j_decompress_ptr cinfo,
   src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
   src->term_source = term_source;
   src->bytes_in_buffer = (size_t) insize;
-  src->next_input_byte = (JOCTET *) inbuffer;
+  src->next_input_byte = (const JOCTET *) inbuffer;
 }
 #endif
diff --git a/jpeglib.h b/jpeglib.h
index 63f312c1..ddf637fb 100644
--- a/jpeglib.h
+++ b/jpeglib.h
@@ -966,7 +966,7 @@ EXTERN(void) jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile);
 /* Data source and destination managers: memory buffers. */
 EXTERN(void) jpeg_mem_dest (j_compress_ptr cinfo, unsigned char ** outbuffer,
                             unsigned long * outsize);
-EXTERN(void) jpeg_mem_src (j_decompress_ptr cinfo, unsigned char * inbuffer,
+EXTERN(void) jpeg_mem_src (j_decompress_ptr cinfo, const unsigned char * inbuffer,
                            unsigned long insize);
 #endif
 
@@ -1046,10 +1046,10 @@ EXTERN(JDIMENSION) jpeg_read_raw_data (j_decompress_ptr cinfo, JSAMPIMAGE data,
                                        JDIMENSION max_lines);
 
 /* Additional entry points for buffered-image mode. */
-EXTERN(boolean) jpeg_has_multiple_scans (j_decompress_ptr cinfo);
+EXTERN(boolean) jpeg_has_multiple_scans (const j_decompress_ptr cinfo);
 EXTERN(boolean) jpeg_start_output (j_decompress_ptr cinfo, int scan_number);
 EXTERN(boolean) jpeg_finish_output (j_decompress_ptr cinfo);
-EXTERN(boolean) jpeg_input_complete (j_decompress_ptr cinfo);
+EXTERN(boolean) jpeg_input_complete (const j_decompress_ptr cinfo);
 EXTERN(void) jpeg_new_colormap (j_decompress_ptr cinfo);
 EXTERN(int) jpeg_consume_input (j_decompress_ptr cinfo);
 /* Return value is one of: */
@@ -1078,7 +1078,7 @@ EXTERN(void) jpeg_set_marker_processor (j_decompress_ptr cinfo,
 EXTERN(jvirt_barray_ptr *) jpeg_read_coefficients (j_decompress_ptr cinfo);
 EXTERN(void) jpeg_write_coefficients (j_compress_ptr cinfo,
                                       jvirt_barray_ptr * coef_arrays);
-EXTERN(void) jpeg_copy_critical_parameters (j_decompress_ptr srcinfo,
+EXTERN(void) jpeg_copy_critical_parameters (const j_decompress_ptr srcinfo,
                                             j_compress_ptr dstinfo);
 
 /* If you choose to abort compression or decompression before completing
@@ -1100,25 +1100,25 @@ EXTERN(void) jpeg_destroy (j_common_ptr cinfo);
 EXTERN(boolean) jpeg_resync_to_restart (j_decompress_ptr cinfo, int desired);
 
 /* Accessor functions for extension parameters */
-EXTERN(boolean) jpeg_c_bool_param_supported (j_compress_ptr cinfo,
+EXTERN(boolean) jpeg_c_bool_param_supported (const j_compress_ptr cinfo,
                                              J_BOOLEAN_PARAM param);
 EXTERN(void) jpeg_c_set_bool_param (j_compress_ptr cinfo,
                                     J_BOOLEAN_PARAM param, boolean value);
-EXTERN(boolean) jpeg_c_get_bool_param (j_compress_ptr cinfo,
+EXTERN(boolean) jpeg_c_get_bool_param (const j_compress_ptr cinfo,
                                        J_BOOLEAN_PARAM param);
 
-EXTERN(boolean) jpeg_c_float_param_supported (j_compress_ptr cinfo,
+EXTERN(boolean) jpeg_c_float_param_supported (const j_compress_ptr cinfo,
                                               J_FLOAT_PARAM param);
 EXTERN(void) jpeg_c_set_float_param (j_compress_ptr cinfo, J_FLOAT_PARAM param,
                                      float value);
-EXTERN(float) jpeg_c_get_float_param (j_compress_ptr cinfo,
+EXTERN(float) jpeg_c_get_float_param (const j_compress_ptr cinfo,
                                       J_FLOAT_PARAM param);
 
-EXTERN(boolean) jpeg_c_int_param_supported (j_compress_ptr cinfo,
+EXTERN(boolean) jpeg_c_int_param_supported (const j_compress_ptr cinfo,
                                             J_INT_PARAM param);
 EXTERN(void) jpeg_c_set_int_param (j_compress_ptr cinfo, J_INT_PARAM param,
                                    int value);
-EXTERN(int) jpeg_c_get_int_param (j_compress_ptr cinfo, J_INT_PARAM param);
+EXTERN(int) jpeg_c_get_int_param (const j_compress_ptr cinfo, J_INT_PARAM param);
 
 
 /* These marker codes are exported since applications and data source modules