diff --git a/src/polyp/error.c b/src/polyp/error.c
index ee9ce51b1..0e3b506f1 100644
--- a/src/polyp/error.c
+++ b/src/polyp/error.c
@@ -170,7 +170,7 @@ static char *tlsstr;
 
 #endif
 
-char* pa_cstrerror(int errnum) {
+const char* pa_cstrerror(int errnum) {
     const char *origbuf;
 
 #ifdef HAVE_STRERROR_R
diff --git a/src/polyp/error.h b/src/polyp/error.h
index 33507bfd4..1d7b2ca64 100644
--- a/src/polyp/error.h
+++ b/src/polyp/error.h
@@ -37,7 +37,7 @@ const char* pa_strerror(int error);
  * string to UTF-8. The function is thread safe but the returned string is
  * only guaranteed to exist until the thread exits or pa_cstrerror() is
  * called again from the same thread. */
-char* pa_cstrerror(int errnum);
+const char* pa_cstrerror(int errnum);
 
 PA_C_DECL_END