diff --git a/lib/cretonne/src/regalloc/allocatable_set.rs b/lib/cretonne/src/regalloc/allocatable_set.rs
index aecd338e7f..063c8e63ac 100644
--- a/lib/cretonne/src/regalloc/allocatable_set.rs
+++ b/lib/cretonne/src/regalloc/allocatable_set.rs
@@ -5,7 +5,8 @@
 //! "register unit" abstraction. Every register contains one or more register units. Registers that
 //! share a register unit can't be in use at the same time.
 
-use isa::registers::{RegUnit, RegUnitMask, RegClass};
+use isa::registers::{RegInfo, RegUnit, RegUnitMask, RegClass};
+use std::fmt;
 use std::iter::ExactSizeIterator;
 use std::mem::size_of_val;
 
@@ -98,6 +99,12 @@ impl AllocatableSet {
             *x &= y;
         }
     }
+
+    /// Return an object that can display this register set, using the register info from the
+    /// target ISA.
+    pub fn display<'a, R: Into<Option<&'a RegInfo>>>(&self, regs: R) -> DisplayAllocatableSet<'a> {
+        DisplayAllocatableSet(self.clone(), regs.into())
+    }
 }
 
 /// Iterator over available registers in a register class.
@@ -138,6 +145,45 @@ impl Iterator for RegSetIter {
 
 impl ExactSizeIterator for RegSetIter {}
 
+/// Displaying an `AllocatableSet` correctly requires the associated `RegInfo` from the target ISA.
+pub struct DisplayAllocatableSet<'a>(AllocatableSet, Option<&'a RegInfo>);
+
+impl<'a> fmt::Display for DisplayAllocatableSet<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "[")?;
+        match self.1 {
+            None => {
+                for w in &self.0.avail {
+                    write!(f, " #{:08x}", w)?;
+                }
+            }
+            Some(reginfo) => {
+                let toprcs = reginfo
+                    .banks
+                    .iter()
+                    .map(|b| b.first_toprc + b.num_toprcs)
+                    .max()
+                    .expect("No register banks");
+                for rc in &reginfo.classes[0..toprcs] {
+                    if rc.width == 1 {
+                        write!(f, " {}:", rc)?;
+                        for u in self.0.iter(rc) {
+                            write!(f, " {}", reginfo.display_regunit(u))?;
+                        }
+                    }
+                }
+            }
+        }
+        write!(f, " ]")
+    }
+}
+
+impl fmt::Display for AllocatableSet {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.display(None).fmt(f)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/lib/cretonne/src/regalloc/coloring.rs b/lib/cretonne/src/regalloc/coloring.rs
index 4ebf3340f9..e4e5a6599f 100644
--- a/lib/cretonne/src/regalloc/coloring.rs
+++ b/lib/cretonne/src/regalloc/coloring.rs
@@ -278,7 +278,9 @@ impl<'a> Context<'a> {
                   regs: &mut AllocatableSet,
                   locations: &mut ValueLocations,
                   func_signature: &Signature) {
-        dbg!("Coloring {}", dfg.display_inst(inst));
+        dbg!("Coloring {}\n          {}",
+             dfg.display_inst(inst),
+             regs.display(&self.reginfo));
 
         // EBB whose arguments should be colored to match the current branch instruction's
         // arguments.