diff --git a/boards/st/stm32h745i_disco/stm32h745i_disco_stm32h745xx_m7.dts b/boards/st/stm32h745i_disco/stm32h745i_disco_stm32h745xx_m7.dts
index 66f7d4d4163f3..1a8c0a94d94e8 100644
--- a/boards/st/stm32h745i_disco/stm32h745i_disco_stm32h745xx_m7.dts
+++ b/boards/st/stm32h745i_disco/stm32h745i_disco_stm32h745xx_m7.dts
@@ -37,7 +37,8 @@
 	sdram2: sdram@d0000000 {
 		compatible = "zephyr,memory-region", "mmio-sram";
 		device_type = "memory";
-		reg = <0xd0000000 DT_SIZE_M(16)>; /* 128Mbit */
+		/* 128Mbit, but only half is available by HW design */
+		reg = <0xd0000000 DT_SIZE_M(8)>;
 		zephyr,memory-region = "SDRAM2";
 		zephyr,memory-attr = <DT_MEM_ARM(ATTR_MPU_RAM)>;
 	};
diff --git a/boards/st/stm32h750b_dk/stm32h750b_dk-common.dtsi b/boards/st/stm32h750b_dk/stm32h750b_dk-common.dtsi
index bfc806f3e7577..bb16bfba15669 100644
--- a/boards/st/stm32h750b_dk/stm32h750b_dk-common.dtsi
+++ b/boards/st/stm32h750b_dk/stm32h750b_dk-common.dtsi
@@ -20,7 +20,8 @@
 	sdram2: sdram@d0000000 {
 		compatible = "zephyr,memory-region", "mmio-sram";
 		device_type = "memory";
-		reg = <0xd0000000 DT_SIZE_M(16)>; /* 128Mbit */
+		/* 128Mbit, but only half is available by HW design */
+		reg = <0xd0000000 DT_SIZE_M(8)>;
 		zephyr,memory-region = "SDRAM2";
 		zephyr,memory-attr = <DT_MEM_ARM(ATTR_MPU_RAM)>;
 	};