diff --git a/platformio.ini b/platformio.ini
index 9fbcb0a4..f3caa585 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -352,6 +352,7 @@ platform_packages = ${common.platform_packages}
 board_build.ldscript = ${common.ldscript_1m128k}
 build_unflags = ${common.build_unflags}
 build_flags = ${common.build_flags_esp8266} -D WLED_RELEASE_NAME=ESP01 -D WLED_DISABLE_OTA
+  ; -D WLED_USE_UNREAL_MATH ;; may cause wrong sunset/sunrise times, but saves 7064 bytes FLASH and 975 bytes RAM
 lib_deps = ${esp8266.lib_deps}
 
 [env:esp07]
@@ -605,6 +606,7 @@ build_flags = ${common.build_flags} ${esp32s2.build_flags} -D WLED_RELEASE_NAME=
   -DARDUINO_USB_DFU_ON_BOOT=0
   -DLOLIN_WIFI_FIX ; seems to work much better with this
   -D WLED_USE_PSRAM
+  ; -D WLED_USE_UNREAL_MATH ;; may cause wrong sunset/sunrise times, but saves 6792 bytes FLASH
   -D WLED_WATCHDOG_TIMEOUT=0
   -D CONFIG_ASYNC_TCP_USE_WDT=0
   -D LEDPIN=16
diff --git a/wled00/ntp.cpp b/wled00/ntp.cpp
index 471e5f07..c9c4874b 100644
--- a/wled00/ntp.cpp
+++ b/wled00/ntp.cpp
@@ -2,6 +2,21 @@
 #include "wled.h"
 #include "fcn_declare.h"
 
+// on esp8266, building with `-D WLED_USE_UNREAL_MATH` saves around 7Kb flash and 1KB RAM
+//  warning: causes errors in sunset calculations, see #3400
+#if defined(WLED_USE_UNREAL_MATH)
+#define sinf sin_t
+#define asinf asin_t
+#define cosf cos_t
+#define acosf acos_t
+#define tanf tan_t
+#define atanf atan_t
+#define fmodf fmod_t
+#define floorf floor_t
+#else
+#include <math.h>
+#endif
+
 /*
  * Acquires time from NTP server
  */
@@ -426,7 +441,7 @@ int getSunriseUTC(int year, int month, int day, float lat, float lon, bool sunse
   float L = fmodf(M + (1.916f * sinf(DEG_TO_RAD*M)) + (0.02f * sinf(2*DEG_TO_RAD*M)) + 282.634f, 360.0f);
 
   //5a. calculate the Sun's right ascension
-  float RA = fmodf(RAD_TO_DEG*atan(0.91764f * tan(DEG_TO_RAD*L)), 360.0f);
+  float RA = fmodf(RAD_TO_DEG*atanf(0.91764f * tanf(DEG_TO_RAD*L)), 360.0f);
 
   //5b. right ascension value needs to be in the same quadrant as L
   float Lquadrant  = floorf( L/90) * 90;