diff --git a/src/resources/i2c_esp32.cc b/src/resources/i2c_esp32.cc
index 67702c9cf..ba7c8f500 100644
--- a/src/resources/i2c_esp32.cc
+++ b/src/resources/i2c_esp32.cc
@@ -135,9 +135,10 @@ static Object* write_i2c(Process* process, I2cResourceGroup* i2c, int i2c_addres
 
   const uint8* data = buffer.address();
   word length = buffer.length();
-  if (!esp_ptr_internal(data)) {
-    // Copy buffer to malloc heap, if the buffer is not in memory.
-    uint8* copy = unvoid_cast<uint8*>(malloc(length));
+  if (length > 0 && !esp_ptr_internal(data)) {
+    // Copy buffer to internal malloc heap, if the buffer is not in memory.
+    const int caps_flags = MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT;
+    uint8* copy = unvoid_cast<uint8*>(heap_caps_malloc(length, caps_flags));
     if (copy == null) FAIL(MALLOC_FAILED);
     memcpy(copy, data, length);
     data = copy;
diff --git a/src/resources/uart_esp32.cc b/src/resources/uart_esp32.cc
index 04864fb48..3cf138925 100644
--- a/src/resources/uart_esp32.cc
+++ b/src/resources/uart_esp32.cc
@@ -822,12 +822,12 @@ PRIMITIVE(create) {
   }
 
   const int caps_flags = MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT;
-  init.rx_buffer = static_cast<uint8*>(heap_caps_malloc(rx_buffer_size, caps_flags));
+  init.rx_buffer = unvoid_cast<uint8*>(heap_caps_malloc(rx_buffer_size, caps_flags));
   if (!init.rx_buffer) {
     FAIL(MALLOC_FAILED);
   }
 
-  init.tx_buffer = static_cast<uint8*>(heap_caps_malloc(tx_buffer_size, caps_flags));
+  init.tx_buffer = unvoid_cast<uint8*>(heap_caps_malloc(tx_buffer_size, caps_flags));
   if (!init.tx_buffer) {
     FAIL(MALLOC_FAILED);
   }