diff --git a/STATUS.md b/STATUS.md
index 73bd6300..ccb1b8b4 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -226,7 +226,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BBC7`   | `mov_r_FAC1_TMP2`      | PARTIAL  | not fully tested yet                               |
 | `$BBCA`   | `mov_r_FAC1_TMP1`      | PARTIAL  | not fully tested yet                               |
 | `$BBD0`   | `mov_r_FAC1_VAR`       | PARTIAL  | not fully tested yet                               |
-| `$BBD4`   | `mov_r_FAC1_MEM`       | PARTIAL  | not fully tested yet                               |
+| `$BBD4`   | `mov_r_FAC1_MEM`       | DONE     | From the Microsoft BASIC, original name: MOVMF     |
 | `$BBFC`   | `mov_FAC2_FAC1`        | DONE     | From the Microsoft BASIC, original name: MOVFA     |
 | `$BC0C`   | `mov_r_FAC1_FAC2`      | DONE     | From the Microsoft BASIC, original name: MOVAF     |
 | `$BC0F`   | `mov_FAC1_FAC2`        | DONE     | From the Microsoft BASIC, original name: MOVEF     |
diff --git a/src/basic/math_mov/bbd4.mov_r_FAC1_MEM.s b/src/basic/math_mov/bbd4.mov_r_FAC1_MEM.s
index 3fcad9d5..fca7500f 100644
--- a/src/basic/math_mov/bbd4.mov_r_FAC1_MEM.s
+++ b/src/basic/math_mov/bbd4.mov_r_FAC1_MEM.s
@@ -3,16 +3,21 @@
 ;; #LAYOUT# *   BASIC_0 #TAKE
 ;; #LAYOUT# *   *       #IGNORE
 
-;
+; This file is under the MIT license, it contains code released by Microsoft Corporation.
+; See LICENSE for more information.
+
 ; Math package - copy FAC1 to memory location, do not round
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named MOVMF.
+;
 ; Input:
 ; - .X - address low byte
 ; - .Y - address high byte
 ;
 ; Output:
 ; - .A - FAC1 exponent
-;
+; - .Y - 0
+
 ; See also:
 ; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
 ; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
@@ -20,7 +25,25 @@
 
 mov_r_FAC1_MEM:
 	
-	; Start by rounding FAC1
-
-	jsr round_FAC1
-	jmp mov_FAC1_MEM
+    jsr round_FAC1
+    stx INDEX+0
+    sty INDEX+1
+    ldy #4
+    lda FAC1_mantissa+3
+    sta (INDEX),y
+    dey
+    lda FAC1_mantissa+2
+    sta (INDEX),y
+    dey
+    lda FAC1_mantissa+1
+    sta (INDEX),y
+    dey
+    lda FAC1_sign
+    ora #$7F
+    and FAC1_mantissa
+    sta (INDEX),y
+    dey
+    lda FAC1_exponent
+    sta (INDEX),y
+    sty FACOV
+    rts
diff --git a/tools/similarity.c b/tools/similarity.c
index c0360de4..5b62e59b 100644
--- a/tools/similarity.c
+++ b/tools/similarity.c
@@ -24,7 +24,7 @@ int phase_mask[MAX_SIZE+MAX_SIZE];
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB849, 0xB84F,
-    0xBBFC, 0xBC1A
+    0xBBD4, 0xBC1A
 };