diff --git a/src/bindings/connection.cpp b/src/bindings/connection.cpp
index d6e2ffa41..eecab4cc3 100644
--- a/src/bindings/connection.cpp
+++ b/src/bindings/connection.cpp
@@ -1,8 +1,6 @@
 #include "connection.h"
 #include "error.h"
 
-#include <emscripten/threading.h>
-
 namespace vips {
 
 Source Source::new_from_file(const std::string &filename) {
@@ -35,10 +33,11 @@ int64_t SourceCustom::read_handler(VipsSourceCustom *source, void *buffer,
     if (self->read_callback == nullptr)
         return -1;
 
-    // Ensure that we call the JS function on the main thread, see:
-    // https://github.com/emscripten-core/emscripten/issues/11317
-    int64_t bytes_read = emscripten_sync_run_in_main_runtime_thread(
-        EM_FUNC_SIG_JPJ, self->read_callback, buffer, length);
+    int64_t bytes_read;
+    proxy_sync([&]() {
+        bytes_read = self->read_callback(buffer, length);
+    });
+
     return bytes_read;
 }
 
@@ -48,8 +47,11 @@ int64_t SourceCustom::seek_handler(VipsSourceCustom *source, int64_t offset,
     if (self->seek_callback == nullptr)
         return -1;
 
-    int64_t new_pos = emscripten_sync_run_in_main_runtime_thread(
-        EM_FUNC_SIG_JJI, self->seek_callback, offset, whence);
+    int64_t new_pos;
+    proxy_sync([&]() {
+        new_pos = self->seek_callback(offset, whence);
+    });
+
     return new_pos;
 }
 
@@ -91,8 +93,11 @@ int64_t TargetCustom::write_handler(VipsTargetCustom *target,
     if (self->write_callback == nullptr)
         return -1;
 
-    int64_t bytes_written = emscripten_sync_run_in_main_runtime_thread(
-        EM_FUNC_SIG_JPJ, self->write_callback, buffer, length);
+    int64_t bytes_written;
+    proxy_sync([&]() {
+        bytes_written = self->write_callback(buffer, length);
+    });
+
     return bytes_written;
 }
 
@@ -105,8 +110,11 @@ int64_t TargetCustom::read_handler(VipsTargetCustom *target, void *buffer,
     if (self->read_callback == nullptr)
         return -1;
 
-    int64_t bytes_read = emscripten_sync_run_in_main_runtime_thread(
-        EM_FUNC_SIG_JPJ, self->read_callback, buffer, length);
+    int64_t bytes_read;
+    proxy_sync([&]() {
+        bytes_read = self->read_callback(buffer, length);
+    });
+
     return bytes_read;
 }
 
@@ -116,8 +124,11 @@ int64_t TargetCustom::seek_handler(VipsTargetCustom *target, int64_t offset,
     if (self->seek_callback == nullptr)
         return -1;
 
-    int64_t new_pos = emscripten_sync_run_in_main_runtime_thread(
-        EM_FUNC_SIG_JJI, self->seek_callback, offset, whence);
+    int64_t new_pos;
+    proxy_sync([&]() {
+        new_pos = self->seek_callback(offset, whence);
+    });
+
     return new_pos;
 }
 
@@ -126,9 +137,14 @@ int TargetCustom::end_handler(VipsTargetCustom *target, void *user) {
     if (self->end_callback == nullptr)
         return 0;
 
-    return emscripten_sync_run_in_main_runtime_thread(EM_FUNC_SIG_I,
-                                                      self->end_callback);
+    int result;
+    proxy_sync([&]() {
+        result = self->end_callback();
+    });
+
+    return result;
 }
+
 void TargetCustom::set_write_callback(emscripten::val js_func) {
     emscripten::val ptr = emscripten::val::module_property("addFunction")(
         js_func, emscripten::val("jpj"));
diff --git a/src/bindings/image.cpp b/src/bindings/image.cpp
index 15e038441..1e94bede4 100644
--- a/src/bindings/image.cpp
+++ b/src/bindings/image.cpp
@@ -98,10 +98,9 @@ void Image::eval_handler(VipsImage *image, VipsProgress *progress, void *user) {
     if (self->progress_callback == nullptr)
         return;
 
-    // Ensure that we call the JS function on the main thread, see:
-    // https://github.com/emscripten-core/emscripten/issues/11317
-    emscripten_sync_run_in_main_runtime_thread(
-        EM_FUNC_SIG_VI, self->progress_callback, progress->percent);
+    proxy_sync([&]() {
+        self->progress_callback(progress->percent);
+    });
 }
 
 void Image::set_progress_callback(emscripten::val js_func) {
diff --git a/src/bindings/image.h b/src/bindings/image.h
index d8b2b3be4..e95037509 100644
--- a/src/bindings/image.h
+++ b/src/bindings/image.h
@@ -11,7 +11,6 @@
 #include <vector>
 
 #include <emscripten/val.h>
-#include <emscripten/threading.h>
 
 namespace vips {
 
diff --git a/src/bindings/utils.cpp b/src/bindings/utils.cpp
index 3a8d72928..dbe663a9c 100644
--- a/src/bindings/utils.cpp
+++ b/src/bindings/utils.cpp
@@ -2,6 +2,9 @@
 
 #include "option.h"
 
+#include <emscripten/proxying.h>
+#include <emscripten/threading.h>
+
 namespace vips {
 
 std::vector<int> blend_modes_to_int(emscripten::val v) {
@@ -39,4 +42,15 @@ std::vector<double> invert(const std::vector<double> &vector) {
     return new_vector;
 }
 
+static void run(void *arg) {
+    std::function<void()> *f = reinterpret_cast<std::function<void()> *>(arg);
+    (*f)();
+}
+
+bool proxy_sync(const std::function<void()> &func) {
+    em_proxying_queue *q = emscripten_proxy_get_system_queue();
+    return emscripten_proxy_sync(q, emscripten_main_runtime_thread_id(), run,
+                                 (void *)&func);
+}
+
 }  // namespace vips
diff --git a/src/bindings/utils.h b/src/bindings/utils.h
index 0d6d11062..ce7b0fc46 100644
--- a/src/bindings/utils.h
+++ b/src/bindings/utils.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <functional>
 #include <string>
 #include <vector>
 
@@ -71,4 +72,10 @@ std::vector<double> negate(const std::vector<double> &vector);
 
 std::vector<double> invert(const std::vector<double> &vector);
 
+/**
+ * Ensure that we call JS functions on the main runtime thread, see:
+ * https://github.com/emscripten-core/emscripten/issues/11317
+ */
+bool proxy_sync(const std::function<void()> &func);
+
 }  // namespace vips