diff --git a/il65/astdefs.py b/il65/astdefs.py
index f99dbf9b3..d10b2cd28 100644
--- a/il65/astdefs.py
+++ b/il65/astdefs.py
@@ -307,7 +307,9 @@ class MemMappedValue(Value):
         if self.constant:
             return False, "cannot assign to a constant"
         if isinstance(other, IndirectValue):
-            return False, "can not yet assign memory mapped value from indirect value"  # @todo indirect v assign
+            if self.datatype == other.datatype:
+                return True, ""
+            return False, "data type of value and target are not the same"
         if self.datatype == DataType.BYTE:
             if isinstance(other, (IntegerValue, RegisterValue, MemMappedValue)):
                 if other.datatype == DataType.BYTE:
diff --git a/il65/codegen.py b/il65/codegen.py
index f74a8bf7c..b1a5010c8 100644
--- a/il65/codegen.py
+++ b/il65/codegen.py
@@ -395,13 +395,9 @@ class CodeGenerator:
         self.previous_stmt_was_assignment = isinstance(stmt, AssignmentStmt)
 
     def generate_incr_or_decr(self, stmt: Union[InplaceIncrStmt, InplaceDecrStmt]) -> None:
-        if stmt.what.datatype == DataType.FLOAT:
-            raise CodeError("incr/decr on float not yet supported")  # @todo support incr/decr on float
-        else:
-            assert type(stmt.howmuch) is int
         assert stmt.howmuch > 0
-        if stmt.howmuch > 0xff:
-            raise CodeError("only supports incr/decr by up to 255 for now")   # XXX
+        if stmt.what.datatype != DataType.FLOAT and stmt.howmuch > 0xff:
+            raise CodeError("only supports integer incr/decr by up to 255 for now")   # XXX
         is_incr = isinstance(stmt, InplaceIncrStmt)
         if isinstance(stmt.what, RegisterValue):
             reg = stmt.what.register
@@ -564,8 +560,20 @@ class CodeGenerator:
                         self.p("\t\tbcs  +")
                         self.p("\t\tdec  {:s}+1".format(r_str))
                         self.p("+\t\tpla")
+            elif what.datatype == DataType.FLOAT:
+                if stmt.howmuch == 1.0:
+                    t_str = stmt.what.name or Parser.to_hex(stmt.what.address)
+                    with self.preserving_registers({'A', 'X', 'Y'}, loads_a_within=True):
+                        self.p("\t\t  ldx  #<" + t_str)
+                        self.p("\t\t  ldy  #>" + t_str)
+                        if is_incr:
+                            self.p("\t\t  jsr  il65_lib.float_add_one")
+                        else:
+                            self.p("\t\t  jsr  il65_lib.float_sub_one")
+                else:
+                    raise CodeError("cannot incr/decr float by other than 1 at this time", stmt.howmuch)  # XXX
             else:
-                raise CodeError("cannot in/decrement memory of type " + str(what.datatype))
+                raise CodeError("cannot in/decrement memory of type " + str(what.datatype), stmt.howmuch)
         else:
             raise CodeError("cannot in/decrement " + str(stmt.what))
 
diff --git a/il65/parse.py b/il65/parse.py
index 94bbabfd9..53aa2c4e2 100644
--- a/il65/parse.py
+++ b/il65/parse.py
@@ -1163,7 +1163,7 @@ class Parser:
         if datatype in (DataType.BYTE, DataType.WORD, DataType.MATRIX) and type(value) is float:
             frac = math.modf(value)  # type:ignore
             if frac != 0:
-                self.print_warning("float value truncated")
+                self.print_warning("float value truncated ({} to datatype {})".format(value, datatype.name))
                 return True, int(value)
         return False, value
 
@@ -1333,7 +1333,8 @@ class Optimizer:
     def remove_unused_subroutines(self, block: Block) -> None:
         # some symbols are used by the emitted assembly code from the code generator,
         # and should never be removed or the assembler will fail
-        never_remove = {"c64.GIVUAYF", "c64.FREADUY", "c64.FTOMEMXY"}
+        # @todo make this dynamic
+        never_remove = {"c64.GIVUAYF", "c64.FREADUY", "c64.FTOMEMXY", "c64.FADD", "c64.FSUB"}
         discarded = []
         for sub in list(block.symbols.iter_subroutines()):
             usages = self.parsed.subroutine_usage[(sub.blockname, sub.name)]
diff --git a/lib/il65lib.ill b/lib/il65lib.ill
index 857844744..cc4b594f3 100644
--- a/lib/il65lib.ill
+++ b/lib/il65lib.ill
@@ -121,4 +121,35 @@ copy_mflt	stx  SCRATCH_ZP1
 		ldy  SCRATCH_ZPWORD1+1
 		rts
 	}
+
+	asm  {
+
+; ---- add 1 to the MFLT pointed to by X/Y.  Clobbers A, X, Y
+float_add_one
+		stx  SCRATCH_ZP1
+		sty  SCRATCH_ZP2
+		txa
+		jsr  c64.MOVFM		; fac1 = float XY
+		lda  #<c64.FL_FONE
+		ldy  #>c64.FL_FONE
+		jsr  c64.FADD		; fac1 += 1
+		ldx  SCRATCH_ZP1
+		ldy  SCRATCH_ZP2
+		jmp  c64.FTOMEMXY	; float XY = fac1
+
+; ---- subtract 1 from the MFLT pointed to by X/Y.  Clobbers A, X, Y
+float_sub_one
+		stx  SCRATCH_ZP1
+		sty  SCRATCH_ZP2
+		lda  #<c64.FL_FONE
+		ldy  #>c64.FL_FONE
+		jsr  c64.MOVFM		; fac1 = 1
+		txa
+		ldy  SCRATCH_ZP2
+		jsr  c64.FSUB		; fac1 = float XY - 1
+		ldx  SCRATCH_ZP1
+		ldy  SCRATCH_ZP2
+		jmp  c64.FTOMEMXY	; float XY = fac1
+
+	}
 }
diff --git a/todo.ill b/todo.ill
index 6cc40885e..994143b2e 100644
--- a/todo.ill
+++ b/todo.ill
@@ -5,7 +5,35 @@ output prg,basic
 import "c64lib"
 
 ~ main {
+
+        var     .float  float1  = 123.456
 start
+        c64.MOVFM(#float1)
+        c64.FPRINTLN()
+        float1++
+        c64.MOVFM(#float1)
+        c64.FPRINTLN()
+        float1-=1
+        c64.MOVFM(#float1)
+        c64.FPRINTLN()
+        float1--
+        c64.MOVFM(#float1)
+        c64.FPRINTLN()
+        ;float1+=0.5
+        ;c64.MOVFM(#float1)
+        ;c64.FPRINTLN()
+        ;float1+=2235.55
+        ;c64.MOVFM(#float1)
+        ;c64.FPRINTLN()
+        ;float1-=999.55
+        ;c64.MOVFM(#float1)
+        ;c64.FPRINTLN()
+        ;float1-=33333.456
+        ;c64.MOVFM(#float1)
+        ;c64.FPRINTLN()
+
+        return
+
         A = $11
         X = $22
         Y = $33