diff --git a/CHANGELOG.md b/CHANGELOG.md
index a6fa85ba..c3612675 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ HEAD
 ----
 
 * Fix compatibility with the Zephyr Project (issue #1905)
+* Allow using PROGMEM outside of Arduino (issue #1903)
 
 v6.21.1 (2023-03-27)
 -------
diff --git a/extras/tests/Helpers/Arduino.h b/extras/tests/Helpers/Arduino.h
index 5f6f3fe3..ef3640d9 100644
--- a/extras/tests/Helpers/Arduino.h
+++ b/extras/tests/Helpers/Arduino.h
@@ -7,5 +7,7 @@
 #include "api/Print.h"
 #include "api/Stream.h"
 #include "api/String.h"
+#include "avr/pgmspace.h"
 
+#define ARDUINO
 #define ARDUINO_H_INCLUDED 1
diff --git a/extras/tests/Helpers/progmem_emulation.hpp b/extras/tests/Helpers/avr/pgmspace.h
similarity index 98%
rename from extras/tests/Helpers/progmem_emulation.hpp
rename to extras/tests/Helpers/avr/pgmspace.h
index ecb9f509..378065da 100644
--- a/extras/tests/Helpers/progmem_emulation.hpp
+++ b/extras/tests/Helpers/avr/pgmspace.h
@@ -2,6 +2,8 @@
 // Copyright © 2014-2023, Benoit BLANCHON
 // MIT License
 
+#pragma once
+
 #include <stdint.h>  // uint8_t
 
 #define PROGMEM
diff --git a/extras/tests/Misc/StringAdapters.cpp b/extras/tests/Misc/StringAdapters.cpp
index cc6d681b..1c77e08b 100644
--- a/extras/tests/Misc/StringAdapters.cpp
+++ b/extras/tests/Misc/StringAdapters.cpp
@@ -2,17 +2,16 @@
 // Copyright © 2014-2023, Benoit BLANCHON
 // MIT License
 
-#define ARDUINOJSON_ENABLE_PROGMEM 1
-
-#include "custom_string.hpp"
-#include "progmem_emulation.hpp"
-#include "weird_strcmp.hpp"
+#include <Arduino.h>
 
 #include <ArduinoJson/Strings/IsString.hpp>
 #include <ArduinoJson/Strings/StringAdapters.hpp>
 
 #include <catch.hpp>
 
+#include "custom_string.hpp"
+#include "weird_strcmp.hpp"
+
 using namespace ArduinoJson::detail;
 
 TEST_CASE("ZeroTerminatedRamString") {
diff --git a/extras/tests/Misc/StringWriter.cpp b/extras/tests/Misc/StringWriter.cpp
index 3cc1333f..81cb88e9 100644
--- a/extras/tests/Misc/StringWriter.cpp
+++ b/extras/tests/Misc/StringWriter.cpp
@@ -2,10 +2,13 @@
 // Copyright © 2014-2023, Benoit BLANCHON
 // MIT License
 
-#define ARDUINOJSON_ENABLE_ARDUINO_STRING 1
+#include <Arduino.h>
+
 #define ARDUINOJSON_STRING_BUFFER_SIZE 5
 #include <ArduinoJson.h>
+
 #include <catch.hpp>
+
 #include "custom_string.hpp"
 
 using namespace ArduinoJson::detail;
diff --git a/extras/tests/MixedConfiguration/enable_progmem_1.cpp b/extras/tests/MixedConfiguration/enable_progmem_1.cpp
index 92a3cbf1..2cc683d7 100644
--- a/extras/tests/MixedConfiguration/enable_progmem_1.cpp
+++ b/extras/tests/MixedConfiguration/enable_progmem_1.cpp
@@ -2,8 +2,6 @@
 // Copyright © 2014-2023, Benoit BLANCHON
 // MIT License
 
-#include "progmem_emulation.hpp"
-
 #define ARDUINOJSON_ENABLE_PROGMEM 1
 #include <ArduinoJson.h>
 
diff --git a/extras/tests/MixedConfiguration/enable_string_deduplication_0.cpp b/extras/tests/MixedConfiguration/enable_string_deduplication_0.cpp
index d763eec1..7277af94 100644
--- a/extras/tests/MixedConfiguration/enable_string_deduplication_0.cpp
+++ b/extras/tests/MixedConfiguration/enable_string_deduplication_0.cpp
@@ -2,8 +2,6 @@
 // Copyright © 2014-2023, Benoit BLANCHON
 // MIT License
 
-#include "progmem_emulation.hpp"
-
 #define ARDUINOJSON_ENABLE_ARDUINO_STRING 1
 #define ARDUINOJSON_ENABLE_PROGMEM 1
 #define ARDUINOJSON_ENABLE_STRING_DEDUPLICATION 0
diff --git a/extras/tests/MixedConfiguration/enable_string_deduplication_1.cpp b/extras/tests/MixedConfiguration/enable_string_deduplication_1.cpp
index a8388a96..d3b2285e 100644
--- a/extras/tests/MixedConfiguration/enable_string_deduplication_1.cpp
+++ b/extras/tests/MixedConfiguration/enable_string_deduplication_1.cpp
@@ -2,8 +2,6 @@
 // Copyright © 2014-2023, Benoit BLANCHON
 // MIT License
 
-#include "progmem_emulation.hpp"
-
 #define ARDUINOJSON_ENABLE_ARDUINO_STRING 1
 #define ARDUINOJSON_ENABLE_PROGMEM 1
 #define ARDUINOJSON_ENABLE_STRING_DEDUPLICATION 1
diff --git a/extras/tests/MixedConfiguration/issue1707.cpp b/extras/tests/MixedConfiguration/issue1707.cpp
index f3ab7f9f..f8ca566b 100644
--- a/extras/tests/MixedConfiguration/issue1707.cpp
+++ b/extras/tests/MixedConfiguration/issue1707.cpp
@@ -5,8 +5,6 @@
 #define ARDUINO
 #define memcpy_P(dest, src, n) memcpy((dest), (src), (n))
 
-#include "progmem_emulation.hpp"
-
 #include <ArduinoJson.h>
 
 #include <catch.hpp>
diff --git a/src/ArduinoJson.hpp b/src/ArduinoJson.hpp
index 0c8832a1..2d1b0be1 100644
--- a/src/ArduinoJson.hpp
+++ b/src/ArduinoJson.hpp
@@ -13,7 +13,8 @@
 // Include Arduino.h before stdlib.h to avoid conflict with atexit()
 // https://github.com/bblanchon/ArduinoJson/pull/1693#issuecomment-1001060240
 #if ARDUINOJSON_ENABLE_ARDUINO_STRING || ARDUINOJSON_ENABLE_ARDUINO_STREAM || \
-    ARDUINOJSON_ENABLE_ARDUINO_PRINT || ARDUINOJSON_ENABLE_PROGMEM
+    ARDUINOJSON_ENABLE_ARDUINO_PRINT ||                                       \
+    (ARDUINOJSON_ENABLE_PROGMEM && defined(ARDUINO))
 #  include <Arduino.h>
 #endif
 
diff --git a/src/ArduinoJson/Deserialization/Readers/FlashReader.hpp b/src/ArduinoJson/Deserialization/Readers/FlashReader.hpp
index df2314ef..97714afb 100644
--- a/src/ArduinoJson/Deserialization/Readers/FlashReader.hpp
+++ b/src/ArduinoJson/Deserialization/Readers/FlashReader.hpp
@@ -4,7 +4,7 @@
 
 #pragma once
 
-#include <Arduino.h>
+#include <ArduinoJson/Polyfills/pgmspace.hpp>
 
 ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
diff --git a/src/ArduinoJson/Polyfills/pgmspace.hpp b/src/ArduinoJson/Polyfills/pgmspace.hpp
index 03adc6f1..9e66f96a 100644
--- a/src/ArduinoJson/Polyfills/pgmspace.hpp
+++ b/src/ArduinoJson/Polyfills/pgmspace.hpp
@@ -4,7 +4,13 @@
 
 #pragma once
 
-#include <Arduino.h>
+#ifdef ARDUINO
+#  include <Arduino.h>
+#else
+// Allow using PROGMEM outside of Arduino (issue #1903)
+class __FlashStringHelper;
+#  include <avr/pgmspace.h>
+#endif
 
 #include <ArduinoJson/Configuration.hpp>
 #include <ArduinoJson/Namespace.hpp>
diff --git a/src/ArduinoJson/Strings/Adapters/FlashString.hpp b/src/ArduinoJson/Strings/Adapters/FlashString.hpp
index eaffe7e3..4989315a 100644
--- a/src/ArduinoJson/Strings/Adapters/FlashString.hpp
+++ b/src/ArduinoJson/Strings/Adapters/FlashString.hpp
@@ -4,8 +4,6 @@
 
 #pragma once
 
-#include <Arduino.h>
-
 #include <ArduinoJson/Polyfills/pgmspace.hpp>
 #include <ArduinoJson/Strings/StringAdapter.hpp>