diff --git a/os/hal/ports/SAMA/SAMA5D2x/sama_matrix.c b/os/hal/ports/SAMA/SAMA5D2x/sama_matrix.c
index da6f6f340..c24f8a703 100644
--- a/os/hal/ports/SAMA/SAMA5D2x/sama_matrix.c
+++ b/os/hal/ports/SAMA/SAMA5D2x/sama_matrix.c
@@ -171,11 +171,14 @@ void mtxSetSlaveSplitAddr(Matrix *mtxp, uint8_t slaveID,
   mtxDisableWP(mtxp);
   uint8_t i = mask, j = 0;
   uint32_t value = 0;
+  uint32_t pmask = 0;
   for (i = 1; (i <= mask) && (j < 32); i <<= 1, j += 4) {
-    if (i & mask)
+    if (i & mask) {
       value |= areaSize << j;
+      pmask |= 0x0F << j;
+    }
   }
-  mtxp->MATRIX_SASSR[slaveID] = value;
+  mtxp->MATRIX_SASSR[slaveID] = (mtxp->MATRIX_SASSR[slaveID] & ~pmask) | value;
   mtxEnableWP(mtxp);
 }
 
@@ -196,11 +199,14 @@ void mtxSetSlaveRegionSize(Matrix *mtxp, uint8_t slaveID,
   mtxDisableWP(mtxp);
   uint8_t i = mask, j = 0;
   uint32_t value = 0;
+  uint32_t pmask = 0;
   for (i = 1; (i <= mask) && (j < 32 ); i <<= 1, j += 4) {
-    if (i & mask)
+    if (i & mask) {
       value |= areaSize << j;
+      pmask |= 0x0F << j;
+    }
   }
-  mtxp->MATRIX_SRTSR[slaveID] = value;
+  mtxp->MATRIX_SRTSR[slaveID] = (mtxp->MATRIX_SRTSR[slaveID] & ~pmask) | value;
   mtxEnableWP(mtxp);
 }