diff --git a/esphome/components/sha256/sha256.cpp b/esphome/components/sha256/sha256.cpp
index 94f623f2fa..a3e06cae2f 100644
--- a/esphome/components/sha256/sha256.cpp
+++ b/esphome/components/sha256/sha256.cpp
@@ -2,19 +2,9 @@
 #include "esphome/core/helpers.h"
 #include <cstring>
 
-#ifdef USE_ESP32
-#include "mbedtls/sha256.h"
-#elif defined(USE_ARDUINO)
-#include <SHA256.h>
-#endif
-
 namespace esphome::sha256 {
 
 #ifdef USE_ESP32
-struct SHA256::SHA256Context {
-  mbedtls_sha256_context ctx;
-  uint8_t hash[32];
-};
 
 SHA256::~SHA256() {
   if (this->ctx_) {
@@ -46,12 +36,6 @@ void SHA256::calculate() {
 
 #elif defined(USE_ARDUINO)
 
-struct SHA256::SHA256Context {
-  ::SHA256 sha;
-  uint8_t hash[32];
-  bool calculated{false};
-};
-
 SHA256::~SHA256() = default;
 
 void SHA256::init() {
diff --git a/esphome/components/sha256/sha256.h b/esphome/components/sha256/sha256.h
index dd1742ea0d..5917f68572 100644
--- a/esphome/components/sha256/sha256.h
+++ b/esphome/components/sha256/sha256.h
@@ -5,6 +5,12 @@
 #include <string>
 #include <memory>
 
+#ifdef USE_ESP32
+#include "mbedtls/sha256.h"
+#elif defined(USE_ARDUINO)
+#include <SHA256.h>
+#endif
+
 namespace esphome::sha256 {
 
 class SHA256 {
@@ -27,7 +33,20 @@ class SHA256 {
   bool equals_hex(const char *expected);
 
  protected:
-  struct SHA256Context;
+#ifdef USE_ESP32
+  struct SHA256Context {
+    mbedtls_sha256_context ctx;
+    uint8_t hash[32];
+  };
+#elif defined(USE_ARDUINO)
+  struct SHA256Context {
+    ::SHA256 sha;
+    uint8_t hash[32];
+    bool calculated{false};
+  };
+#else
+#error "SHA256 not supported on this platform"
+#endif
   std::unique_ptr<SHA256Context> ctx_;
 };