diff --git a/src/basic/math/b947.inv_FAC1.s b/src/basic/math/b947.inv_FAC1.s
index c97d3b7b..e9f2443e 100644
--- a/src/basic/math/b947.inv_FAC1.s
+++ b/src/basic/math/b947.inv_FAC1.s
@@ -39,6 +39,7 @@ inv_FAC1_mantissa:
     lda FACOV
     eor #$FF
     sta FACOV
+    inc FACOV
     bne inc_FAC1_ret
     
     ; Fallthrough to inc_FAC1
diff --git a/src/basic/math/b983.shiftr_FAC.s b/src/basic/math/b983.shiftr_FAC.s
index 6cf67738..ea124828 100644
--- a/src/basic/math/b983.shiftr_FAC.s
+++ b/src/basic/math/b983.shiftr_FAC.s
@@ -45,7 +45,7 @@ shiftr_FAC:
     sbc #8              ; Go back to previous value
     tay
     lda FACOV
-    bcs shiftr_FAC
+    bcs shftrt
 .sext:
     asl 1,X
     bcc @2
diff --git a/src/basic/math/bc1b.round_FAC1.jmp.s b/src/basic/math/bc1b.round_FAC1.jmp.s
index 47f8b624..81b1ef11 100644
--- a/src/basic/math/bc1b.round_FAC1.jmp.s
+++ b/src/basic/math/bc1b.round_FAC1.jmp.s
@@ -5,5 +5,6 @@
 
 ; Just a compatibility jump - our routine is longer than original one
 
-	jmp round_FAC1
+round_FAC1:
+	jmp round_FAC1_impl
 	
diff --git a/src/basic/math/round_FAC1.s b/src/basic/math/round_FAC1.s
index 0b401ef9..e8437d57 100644
--- a/src/basic/math/round_FAC1.s
+++ b/src/basic/math/round_FAC1.s
@@ -12,7 +12,7 @@
 
 ; XXX test this
 
-round_FAC1:
+round_FAC1_impl:
 
 	; If number is 0, do not do anything
 
diff --git a/src/basic/math_mov/bbd0.mov_r_FAC1_VAR.s b/src/basic/math_mov/bbd0.mov_r_FAC1_VAR.s
index 6330dd3b..5c5e5094 100644
--- a/src/basic/math_mov/bbd0.mov_r_FAC1_VAR.s
+++ b/src/basic/math_mov/bbd0.mov_r_FAC1_VAR.s
@@ -20,7 +20,7 @@
 
 mov_r_FAC1_VAR:
 
-	ldx #FORPNT+0
-	ldy #FORPNT+1
+	ldx FORPNT+0
+	ldy FORPNT+1
 
 	; FALLTROUGH to mov_r_FAC1_MEM
diff --git a/src/basic/math_mov/bbfc.mov_FAC2_FAC1.s b/src/basic/math_mov/bbfc.mov_FAC2_FAC1.s
index 7da15a4f..148ccb00 100644
--- a/src/basic/math_mov/bbfc.mov_FAC2_FAC1.s
+++ b/src/basic/math_mov/bbfc.mov_FAC2_FAC1.s
@@ -32,7 +32,7 @@ mov_FAC2_FAC1:
     lda FAC2_sign
 
 mov_FAC2_FAC1_sign:
-    sta FAC2_sign
+    sta FAC1_sign
 
     ; Copy the mantissa and the exponent
 
diff --git a/tools/similarity.c b/tools/similarity.c
index 54ffe503..862b68df 100644
--- a/tools/similarity.c
+++ b/tools/similarity.c
@@ -92,7 +92,11 @@ int main(int argc,char **argv)
   if (basic) {
     for (int i = 0; i < NUM_CHUNKS; i++) {
       for (int addr = microsoft_basic_chunks[i * 2]; addr <= microsoft_basic_chunks[i * 2 + 1]; addr++) {
-        f1[addr - 0xA000] = 0;
+        short index = addr - 0xA000;
+        if (f1[index] != f2[index]) {
+            printf("BASIC does not match MS BASIC at %X (%X != %X)\n", addr, f1[index], f2[index]);
+        }
+        f1[index] = 0;
       }
     }
   }