diff --git a/compiler/res/prog8lib/string.p8 b/compiler/res/prog8lib/string.p8
index 18fcf1069..c9480b4bc 100644
--- a/compiler/res/prog8lib/string.p8
+++ b/compiler/res/prog8lib/string.p8
@@ -190,4 +190,46 @@ _found		sty  P8ZP_SCRATCH_B1
         }}
     }
 
+    asmsub lower(uword st @AY) {
+        ; Lowercases the petscii string in-place.
+        ; (for efficiency, non-letter characters > 128 will also not be left intact,
+        ;  but regular text doesn't usually contain those characters anyway.)
+        %asm {{
+            sta  P8ZP_SCRATCH_W1
+            sty  P8ZP_SCRATCH_W1+1
+            ldy  #0
+-           lda  (P8ZP_SCRATCH_W1),y
+            beq  _done
+            and  #$7f
+            cmp  #97
+            bcc  +
+            cmp  #123
+            bcs  +
+            and  #%11011111
++           sta  (P8ZP_SCRATCH_W1),y
+            iny
+            bne  -
+_done       rts
+        }}
+    }
+
+    asmsub upper(uword st @AY) {
+        ; Uppercases the petscii string in-place.
+        %asm {{
+            sta  P8ZP_SCRATCH_W1
+            sty  P8ZP_SCRATCH_W1+1
+            ldy  #0
+-           lda  (P8ZP_SCRATCH_W1),y
+            beq  _done
+            cmp  #65
+            bcc  +
+            cmp  #91
+            bcs  +
+            ora  #%00100000
++           sta  (P8ZP_SCRATCH_W1),y
+            iny
+            bne  -
+_done       rts
+        }}
+    }
 }
diff --git a/docs/source/libraries.rst b/docs/source/libraries.rst
index cddb38054..a538f1663 100644
--- a/docs/source/libraries.rst
+++ b/docs/source/libraries.rst
@@ -173,6 +173,12 @@ Provides string manipulation routines.
     Often you don't have to call this explicitly and can just write ``string1 = string2``
     but this function is useful if you're dealing with addresses for instance.
 
+``lower(string)``
+    Lowercases the petscii-string in place.
+
+``upper(string)``
+    Uppercases the petscii-string in place.
+
 
 floats
 ------
diff --git a/examples/test.p8 b/examples/test.p8
index 449f6bfa3..6ec24835e 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -12,11 +12,23 @@ main {
         str s2 = "12345 ABCDEF..UVWXYZ ()!@#$%;:&*()-=[]<>\xff\xfa\xeb\xc0\n"
         str s3 = "12345 \x61\x62\x63\x64\x65\x66..\x75\x76\x77\x78\x79\x7a ()!@#$%;:&*()-=[]<>\xff\xfa\xeb\xc0\n"
 
-        lower(s1)
-        lower(s2)
-        lower(s3)
-
         txt.lowercase()
+
+        txt.print(s1)
+        txt.print(s2)
+        txt.print(s3)
+
+        string.lower(s1)
+        string.lower(s2)
+        string.lower(s3)
+        txt.print(s1)
+        txt.print(s2)
+        txt.print(s3)
+
+        string.upper(s1)
+        string.upper(s2)
+        string.upper(s3)
+
         txt.print(s1)
         txt.print(s2)
         txt.print(s3)
@@ -24,49 +36,5 @@ main {
         txt.nl()
     }
 
-    asmsub lower(uword st @AY) clobbers(X) {
-        %asm {{
-            sta  P8ZP_SCRATCH_W1
-            sty  P8ZP_SCRATCH_W1+1
-            ldy  #0
--           lda  (P8ZP_SCRATCH_W1),y
-            beq  _done
-            and  #$7f
-            tax
-            and  #%11100000
-            cmp  #%01100000
-            bne  +
-            txa
-            and  #%11011111
-            tax
-+           txa
-            sta  (P8ZP_SCRATCH_W1),y
-            iny
-            bne  -
-_done       rts
-        }}
-    }
 
-    asmsub upper(uword st @AY) clobbers(X) {
-        %asm {{
-            sta  P8ZP_SCRATCH_W1
-            sty  P8ZP_SCRATCH_W1+1
-            ldy  #0
--           lda  (P8ZP_SCRATCH_W1),y
-            beq  _done
-            and  #$7f
-            tax
-            and  #%11100000
-            cmp  #%01100000
-            bne  +
-            txa
-            and  #%11011111
-            tax
-+           txa
-            sta  (P8ZP_SCRATCH_W1),y
-            iny
-            bne  -
-_done       rts
-        }}
-    }
 }