diff --git a/src/guacenc/encode.c b/src/guacenc/encode.c
index ba4050c7..5c2820c6 100644
--- a/src/guacenc/encode.c
+++ b/src/guacenc/encode.c
@@ -60,8 +60,7 @@ static int guacenc_read_instructions(const char* path, guac_socket* socket) {
 
     /* Continuously read and handle all instructions */
     while (!guac_parser_read(parser, socket, -1)) {
-        guacenc_handle_instruction(parser->opcode, parser->argc,
-                (const char**) parser->argv);
+        guacenc_handle_instruction(parser->opcode, parser->argc, parser->argv);
     }
 
     /* Fail on read/parse error */
diff --git a/src/guacenc/instruction-blob.c b/src/guacenc/instruction-blob.c
index e69fe491..10270e23 100644
--- a/src/guacenc/instruction-blob.c
+++ b/src/guacenc/instruction-blob.c
@@ -28,7 +28,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-int guacenc_handle_blob(int argc, const char** argv) {
+int guacenc_handle_blob(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 2) {
@@ -38,7 +38,7 @@ int guacenc_handle_blob(int argc, const char** argv) {
 
     /* Parse arguments */
     int index = atoi(argv[0]);
-    const char* data = argv[1];
+    char* data = argv[1];
 
     /* STUB */
     guacenc_log(GUAC_LOG_DEBUG, "blob: stream=%i data=[%i chars]",
diff --git a/src/guacenc/instruction-cfill.c b/src/guacenc/instruction-cfill.c
index 2042173c..ff35f756 100644
--- a/src/guacenc/instruction-cfill.c
+++ b/src/guacenc/instruction-cfill.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_cfill(int argc, const char** argv) {
+int guacenc_handle_cfill(int argc, char** argv) {
  
     /* Verify argument count */
     if (argc < 6) {
diff --git a/src/guacenc/instruction-copy.c b/src/guacenc/instruction-copy.c
index ce82e82b..56f90fa2 100644
--- a/src/guacenc/instruction-copy.c
+++ b/src/guacenc/instruction-copy.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_copy(int argc, const char** argv) {
+int guacenc_handle_copy(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 9) {
diff --git a/src/guacenc/instruction-cursor.c b/src/guacenc/instruction-cursor.c
index 8d3a5b34..2b237a25 100644
--- a/src/guacenc/instruction-cursor.c
+++ b/src/guacenc/instruction-cursor.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_cursor(int argc, const char** argv) {
+int guacenc_handle_cursor(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 7) {
diff --git a/src/guacenc/instruction-dispose.c b/src/guacenc/instruction-dispose.c
index 0b280a0f..17bf320e 100644
--- a/src/guacenc/instruction-dispose.c
+++ b/src/guacenc/instruction-dispose.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_dispose(int argc, const char** argv) {
+int guacenc_handle_dispose(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 1) {
diff --git a/src/guacenc/instruction-end.c b/src/guacenc/instruction-end.c
index a99a0e45..55e11a39 100644
--- a/src/guacenc/instruction-end.c
+++ b/src/guacenc/instruction-end.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_end(int argc, const char** argv) {
+int guacenc_handle_end(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 1) {
diff --git a/src/guacenc/instruction-img.c b/src/guacenc/instruction-img.c
index 9e2dd312..5cf2c884 100644
--- a/src/guacenc/instruction-img.c
+++ b/src/guacenc/instruction-img.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_img(int argc, const char** argv) {
+int guacenc_handle_img(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 6) {
@@ -39,7 +39,7 @@ int guacenc_handle_img(int argc, const char** argv) {
     int stream_index = atoi(argv[0]);
     int mask = atoi(argv[1]);
     int layer_index = atoi(argv[2]);
-    const char* mimetype = argv[3];
+    char* mimetype = argv[3];
     int x = atoi(argv[4]);
     int y = atoi(argv[5]);
 
diff --git a/src/guacenc/instruction-move.c b/src/guacenc/instruction-move.c
index 2e916929..5472361b 100644
--- a/src/guacenc/instruction-move.c
+++ b/src/guacenc/instruction-move.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_move(int argc, const char** argv) {
+int guacenc_handle_move(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 5) {
diff --git a/src/guacenc/instruction-rect.c b/src/guacenc/instruction-rect.c
index 85e229f0..f9609ab7 100644
--- a/src/guacenc/instruction-rect.c
+++ b/src/guacenc/instruction-rect.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_rect(int argc, const char** argv) {
+int guacenc_handle_rect(int argc, char** argv) {
  
     /* Verify argument count */
     if (argc < 5) {
diff --git a/src/guacenc/instruction-shade.c b/src/guacenc/instruction-shade.c
index 48e6d7aa..f796c064 100644
--- a/src/guacenc/instruction-shade.c
+++ b/src/guacenc/instruction-shade.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_shade(int argc, const char** argv) {
+int guacenc_handle_shade(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 2) {
diff --git a/src/guacenc/instruction-size.c b/src/guacenc/instruction-size.c
index 7057bcc4..1817bfb1 100644
--- a/src/guacenc/instruction-size.c
+++ b/src/guacenc/instruction-size.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_size(int argc, const char** argv) {
+int guacenc_handle_size(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 3) {
diff --git a/src/guacenc/instruction-transfer.c b/src/guacenc/instruction-transfer.c
index ae0f4ea7..ff37d282 100644
--- a/src/guacenc/instruction-transfer.c
+++ b/src/guacenc/instruction-transfer.c
@@ -27,7 +27,7 @@
 
 #include <stdlib.h>
 
-int guacenc_handle_transfer(int argc, const char** argv) {
+int guacenc_handle_transfer(int argc, char** argv) {
 
     /* Verify argument count */
     if (argc < 9) {
diff --git a/src/guacenc/instructions.c b/src/guacenc/instructions.c
index 015ed929..81329cf2 100644
--- a/src/guacenc/instructions.c
+++ b/src/guacenc/instructions.c
@@ -45,7 +45,7 @@ guacenc_instruction_handler_mapping guacenc_instruction_handler_map[] = {
 };
 
 int guacenc_handle_instruction(const char* opcode,
-        int argc, const char** argv) {
+        int argc, char** argv) {
 
     /* Search through mapping for instruction handler having given opcode */
     guacenc_instruction_handler_mapping* current = guacenc_instruction_handler_map;
diff --git a/src/guacenc/instructions.h b/src/guacenc/instructions.h
index 0f7951d6..5f8d6728 100644
--- a/src/guacenc/instructions.h
+++ b/src/guacenc/instructions.h
@@ -44,7 +44,7 @@
  *     Zero if the instruction was handled successfully, non-zero if an error
  *     occurs.
  */
-typedef int guacenc_instruction_handler(int argc, const char** argv);
+typedef int guacenc_instruction_handler(int argc, char** argv);
 
 /**
  * Mapping of instruction opcode to corresponding handler function.
@@ -91,8 +91,7 @@ extern guacenc_instruction_handler_mapping guacenc_instruction_handler_map[];
  *     Zero if the instruction was handled successfully, non-zero if an error
  *     occurs.
  */
-int guacenc_handle_instruction(const char* opcode, int argc,
-        const char** argv);
+int guacenc_handle_instruction(const char* opcode, int argc, char** argv);
 
 /**
  * Handler for the Guacamole "blob" instruction.