diff --git a/src/cl65/spawn-amiga.inc b/src/cl65/spawn-amiga.inc
index 4a0278cfa..b244a95ac 100644
--- a/src/cl65/spawn-amiga.inc
+++ b/src/cl65/spawn-amiga.inc
@@ -54,7 +54,7 @@
 
 int spawnvp (int Mode attribute ((unused)),
              const char* File attribute ((unused)),
-             char* const argv [])
+             const char* const argv [])
 /* Execute the given program searching and wait til it terminates. The Mode
  * argument is ignored (compatibility only). The result of the function is
  * the return code of the program. The function will terminate the program
diff --git a/src/cl65/spawn-unix.inc b/src/cl65/spawn-unix.inc
index a0334b8db..093e35935 100644
--- a/src/cl65/spawn-unix.inc
+++ b/src/cl65/spawn-unix.inc
@@ -62,7 +62,7 @@
 
 
 
-int spawnvp (int Mode attribute ((unused)), const char* File, char* const argv [])
+int spawnvp (int Mode attribute ((unused)), const char* File, const char* const argv [])
 /* Execute the given program searching and wait til it terminates. The Mode
  * argument is ignored (compatibility only). The result of the function is
  * the return code of the program. The function will terminate the program
diff --git a/src/cl65/spawn.h b/src/cl65/spawn.h
index 6e75f555d..a9f5d7c3f 100644
--- a/src/cl65/spawn.h
+++ b/src/cl65/spawn.h
@@ -59,7 +59,7 @@
 
 
 
-int spawnvp (int Mode, const char* File, char* const argv []);
+int spawnvp (int Mode, const char* File, const char* const argv []);
 /* Execute the given program searching and wait til it terminates. The Mode
  * argument is ignored (compatibility only). The result of the function is
  * the return code of the program. The function will terminate the program