diff --git a/resolver.c b/resolver.c
index 34a0bb6..54acc7b 100644
--- a/resolver.c
+++ b/resolver.c
@@ -36,7 +36,7 @@ typedef struct g_proxy_resolver_s {
     // Library reference count
     int32_t ref_count;
     // Proxy resolver interface
-    proxy_resolver_i_s *proxy_resolver_i;
+    const proxy_resolver_i_s *proxy_resolver_i;
     // Thread pool
     void *threadpool;
 } g_proxy_resolver_s;
diff --git a/resolver_gnome3.c b/resolver_gnome3.c
index 0c25e4d..c593ea6 100644
--- a/resolver_gnome3.c
+++ b/resolver_gnome3.c
@@ -260,8 +260,8 @@ bool proxy_resolver_gnome3_global_cleanup(void) {
     return true;
 }
 
-proxy_resolver_i_s *proxy_resolver_gnome3_get_interface(void) {
-    static proxy_resolver_i_s proxy_resolver_gnome3_i = {
+const proxy_resolver_i_s *proxy_resolver_gnome3_get_interface(void) {
+    static const proxy_resolver_i_s proxy_resolver_gnome3_i = {
         proxy_resolver_gnome3_get_proxies_for_url,
         proxy_resolver_gnome3_get_list,
         proxy_resolver_gnome3_get_error,
diff --git a/resolver_gnome3.h b/resolver_gnome3.h
index 1b55c51..dfe8b76 100644
--- a/resolver_gnome3.h
+++ b/resolver_gnome3.h
@@ -12,4 +12,4 @@ bool proxy_resolver_gnome3_delete(void **ctx);
 bool proxy_resolver_gnome3_global_init(void);
 bool proxy_resolver_gnome3_global_cleanup(void);
 
-proxy_resolver_i_s *proxy_resolver_gnome3_get_interface(void);
+const proxy_resolver_i_s *proxy_resolver_gnome3_get_interface(void);
diff --git a/resolver_mac.c b/resolver_mac.c
index d2c7db1..b63423e 100644
--- a/resolver_mac.c
+++ b/resolver_mac.c
@@ -243,8 +243,8 @@ bool proxy_resolver_mac_global_cleanup(void) {
     return true;
 }
 
-proxy_resolver_i_s *proxy_resolver_mac_get_interface(void) {
-    static proxy_resolver_i_s proxy_resolver_mac_i = {
+const proxy_resolver_i_s *proxy_resolver_mac_get_interface(void) {
+    static const proxy_resolver_i_s proxy_resolver_mac_i = {
         proxy_resolver_mac_get_proxies_for_url,
         proxy_resolver_mac_get_list,
         proxy_resolver_mac_get_error,
diff --git a/resolver_mac.h b/resolver_mac.h
index 3af06d7..1a2ad4e 100644
--- a/resolver_mac.h
+++ b/resolver_mac.h
@@ -12,4 +12,4 @@ bool proxy_resolver_mac_delete(void **ctx);
 bool proxy_resolver_mac_global_init(void);
 bool proxy_resolver_mac_global_cleanup(void);
 
-proxy_resolver_i_s *proxy_resolver_mac_get_interface(void);
+const proxy_resolver_i_s *proxy_resolver_mac_get_interface(void);
diff --git a/resolver_posix.c b/resolver_posix.c
index d0cac3c..ee13520 100644
--- a/resolver_posix.c
+++ b/resolver_posix.c
@@ -287,8 +287,8 @@ bool proxy_resolver_posix_global_cleanup(void) {
     return true;
 }
 
-proxy_resolver_i_s *proxy_resolver_posix_get_interface(void) {
-    static proxy_resolver_i_s proxy_resolver_posix_i = {
+const proxy_resolver_i_s *proxy_resolver_posix_get_interface(void) {
+    static const proxy_resolver_i_s proxy_resolver_posix_i = {
         proxy_resolver_posix_get_proxies_for_url,
         proxy_resolver_posix_get_list,
         proxy_resolver_posix_get_error,
diff --git a/resolver_posix.h b/resolver_posix.h
index e7884e4..5eb677b 100644
--- a/resolver_posix.h
+++ b/resolver_posix.h
@@ -14,4 +14,4 @@ bool proxy_resolver_posix_global_init(void);
 bool proxy_resolver_posix_init_ex(void *threadpool);
 bool proxy_resolver_posix_global_cleanup(void);
 
-proxy_resolver_i_s *proxy_resolver_posix_get_interface(void);
+const proxy_resolver_i_s *proxy_resolver_posix_get_interface(void);
diff --git a/resolver_win8.c b/resolver_win8.c
index 41dd9f2..60f8508 100644
--- a/resolver_win8.c
+++ b/resolver_win8.c
@@ -355,8 +355,8 @@ bool proxy_resolver_win8_global_cleanup(void) {
     return true;
 }
 
-proxy_resolver_i_s *proxy_resolver_win8_get_interface(void) {
-    static proxy_resolver_i_s proxy_resolver_win8_i = {
+const proxy_resolver_i_s *proxy_resolver_win8_get_interface(void) {
+    static const proxy_resolver_i_s proxy_resolver_win8_i = {
         proxy_resolver_win8_get_proxies_for_url,
         proxy_resolver_win8_get_list,
         proxy_resolver_win8_get_error,
diff --git a/resolver_win8.h b/resolver_win8.h
index a48c183..97b193c 100644
--- a/resolver_win8.h
+++ b/resolver_win8.h
@@ -12,4 +12,4 @@ bool proxy_resolver_win8_delete(void **ctx);
 bool proxy_resolver_win8_global_init(void);
 bool proxy_resolver_win8_global_cleanup(void);
 
-proxy_resolver_i_s *proxy_resolver_win8_get_interface(void);
+const proxy_resolver_i_s *proxy_resolver_win8_get_interface(void);
diff --git a/resolver_winrt.c b/resolver_winrt.c
index 1365951..0be22e3 100644
--- a/resolver_winrt.c
+++ b/resolver_winrt.c
@@ -409,17 +409,18 @@ bool proxy_resolver_winrt_global_cleanup(void) {
     return true;
 }
 
-proxy_resolver_i_s *proxy_resolver_winrt_get_interface(void) {
-    static proxy_resolver_i_s proxy_resolver_winrt_i = {proxy_resolver_winrt_get_proxies_for_url,
-                                                        proxy_resolver_winrt_get_list,
-                                                        proxy_resolver_winrt_get_error,
-                                                        proxy_resolver_winrt_wait,
-                                                        proxy_resolver_winrt_cancel,
-                                                        proxy_resolver_winrt_create,
-                                                        proxy_resolver_winrt_delete,
-                                                        true,  // get_proxies_for_url is handled asynchronously
-                                                        true,  // get_proxies_for_url takes into account system config
-                                                        proxy_resolver_winrt_global_init,
-                                                        proxy_resolver_winrt_global_cleanup};
+const proxy_resolver_i_s *proxy_resolver_winrt_get_interface(void) {
+    static const proxy_resolver_i_s proxy_resolver_winrt_i = {
+        proxy_resolver_winrt_get_proxies_for_url,
+        proxy_resolver_winrt_get_list,
+        proxy_resolver_winrt_get_error,
+        proxy_resolver_winrt_wait,
+        proxy_resolver_winrt_cancel,
+        proxy_resolver_winrt_create,
+        proxy_resolver_winrt_delete,
+        true,   // get_proxies_for_url is handled asynchronously
+        false,  // get_proxies_for_url does not take into account system config
+        proxy_resolver_winrt_global_init,
+        proxy_resolver_winrt_global_cleanup};
     return &proxy_resolver_winrt_i;
 }
diff --git a/resolver_winrt.h b/resolver_winrt.h
index 3726566..a3e125c 100644
--- a/resolver_winrt.h
+++ b/resolver_winrt.h
@@ -13,4 +13,4 @@ bool proxy_resolver_winrt_delete(void **ctx);
 bool proxy_resolver_winrt_global_init(void);
 bool proxy_resolver_winrt_global_cleanup(void);
 
-proxy_resolver_i_s *proxy_resolver_winrt_get_interface(void);
+const proxy_resolver_i_s *proxy_resolver_winrt_get_interface(void);
diff --git a/resolver_winxp.c b/resolver_winxp.c
index 2b80759..d72a64a 100644
--- a/resolver_winxp.c
+++ b/resolver_winxp.c
@@ -225,8 +225,8 @@ bool proxy_resolver_winxp_global_cleanup(void) {
     return true;
 }
 
-proxy_resolver_i_s *proxy_resolver_winxp_get_interface(void) {
-    static proxy_resolver_i_s proxy_resolver_winxp_i = {
+const proxy_resolver_i_s *proxy_resolver_winxp_get_interface(void) {
+    static const proxy_resolver_i_s proxy_resolver_winxp_i = {
         proxy_resolver_winxp_get_proxies_for_url,
         proxy_resolver_winxp_get_list,
         proxy_resolver_winxp_get_error,
diff --git a/resolver_winxp.h b/resolver_winxp.h
index 02389a7..1b9642f 100644
--- a/resolver_winxp.h
+++ b/resolver_winxp.h
@@ -12,4 +12,4 @@ bool proxy_resolver_winxp_delete(void **ctx);
 bool proxy_resolver_winxp_global_init(void);
 bool proxy_resolver_winxp_global_cleanup(void);
 
-proxy_resolver_i_s *proxy_resolver_winxp_get_interface(void);
+const proxy_resolver_i_s *proxy_resolver_winxp_get_interface(void);