diff --git a/libsrc/common/strstr.s b/libsrc/common/strstr.s
index 9cc9c0d33..d24f1b0c9 100644
--- a/libsrc/common/strstr.s
+++ b/libsrc/common/strstr.s
@@ -5,16 +5,18 @@
 ;
 
         .export         _strstr, _strcasestr
-        .import         popptr1, _tolower
-        .importzp       ptr1, ptr2, ptr3, ptr4, tmp1, tmp2, tmp3
+        .import         popptr1, return0, tolower_a
+        .importzp       ptr1, ptr2, ptr3, ptr4, tmp1, tmp2
+
+maybe_lower:                    ; Lowercase char in A if needed
+        jmp     tolower_a       ; patched on entry with either JMP or RTS
 
 _strstr:
-        ldy     #$01
+        ldy     #$60            ; RTS
         bne     :+
 _strcasestr:
-        ldy     #$00
-:
-        sty     tmp2            ; Set case sensitivity
+        ldy     #$4C            ; JMP absolute
+:       sty     maybe_lower
 
         sta     ptr2            ; Save needle
         stx     ptr2+1
@@ -31,19 +33,13 @@ _strcasestr:
 ; Search for the beginning of the string (this is not an optimal search
 ; strategy [in fact, it's pretty dumb], but it's simple to implement).
 
-        ldx     tmp2            ; Lowercase if needed
-        bne     :+
-        jsr     _tolower
-
-:       sta     tmp1            ; Save start of needle
+        jsr     maybe_lower     ; Lowercase if needed
+        sta     tmp1            ; Save start of needle
 @L1:    lda     (ptr1),y        ; Get next char from haystack
         beq     @NotFound       ; Jump if end
 
-        ldx     tmp2            ; Lowercase if needed
-        bne     :+
-        jsr     _tolower
-
-:       cmp     tmp1            ; Start of needle found?
+        jsr     maybe_lower     ; Lowercase if needed
+        cmp     tmp1            ; Start of needle found?
         beq     @L2             ; Jump if so
         iny                     ; Next char
         bne     @L1
@@ -74,18 +70,13 @@ _strcasestr:
 @L4:    lda     (ptr4),y        ; Get char from needle
         beq     @Found          ; Jump if end of needle (-> found)
 
-        ldx     tmp2            ; Lowercase if needed
-        bne     :+
-        jsr     _tolower
-:       sta     tmp3
+        jsr     maybe_lower     ; Lowercase if needed
+        sta     tmp2
 
         lda     (ptr3),y        ; Compare with haystack
 
-        ldx     tmp2            ; Lowercase if needed
-        bne     :+
-        jsr     _tolower
-
-:       cmp     tmp3
+        jsr     maybe_lower     ; Lowercase if needed
+        cmp     tmp2
         bne     @L5             ; Jump if not equal
         iny                     ; Next char
         bne     @L4
@@ -107,6 +98,4 @@ _strcasestr:
 ; We reached end of haystack without finding needle
 
 @NotFound:
-        lda     #$00            ; return NULL
-        tax
-        rts
+        jmp     return0         ; return NULL
diff --git a/libsrc/common/tolower.s b/libsrc/common/tolower.s
index 22b030da3..4d02e4dfb 100644
--- a/libsrc/common/tolower.s
+++ b/libsrc/common/tolower.s
@@ -10,13 +10,14 @@
 ; int tolower (int c);
 ;
 
-        .export         _tolower
+        .export         _tolower, tolower_a
         .include        "ctype.inc"
         .import         ctypemaskdirect
 
 _tolower:
         cpx     #$00            ; out of range?
-        bne     @L2             ; if so, return the argument unchanged
+        bne     out             ; if so, return the argument unchanged
+tolower_a:
         pha                     ; save char
         jsr     ctypemaskdirect ; get character classification
         and     #CT_UPPER       ; upper case char?
@@ -25,4 +26,4 @@ _tolower:
         adc     #<('a'-'A')     ; make lower case char (ctypemaskdirect ensures carry clear)
         rts
 @L1:    pla                     ; restore char
-@L2:    rts
+out:    rts