diff --git a/meta/gen_settings.py b/meta/gen_settings.py
index 588c2cf798..c3c4710ea3 100644
--- a/meta/gen_settings.py
+++ b/meta/gen_settings.py
@@ -183,18 +183,18 @@ def gen_constructor(sgrp, parent, fmt):
     """
 
     with fmt.indented('impl Flags {', '}'):
-        args = 'builder: Builder'
+        args = 'builder: &Builder'
         if sgrp.parent:
             p = sgrp.parent
             args = '{}: &{}::Flags, {}'.format(p.name, p.qual_mod, args)
         with fmt.indented(
                 'pub fn new({}) -> Flags {{'.format(args), '}'):
-            fmt.line('let bvec = builder.finish("{}");'.format(sgrp.name))
+            fmt.line('let bvec = builder.state_for("{}");'.format(sgrp.name))
             fmt.line('let mut bytes = [0; {}];'.format(sgrp.byte_size()))
             fmt.line('assert_eq!(bvec.len(), {});'.format(sgrp.settings_size))
             with fmt.indented(
-                    'for (i, b) in bvec.into_iter().enumerate() {', '}'):
-                fmt.line('bytes[i] = b;')
+                    'for (i, b) in bvec.iter().enumerate() {', '}'):
+                fmt.line('bytes[i] = *b;')
 
             # Stop here without predicates.
             if len(sgrp.predicate_number) == sgrp.boolean_settings:
diff --git a/src/libcretonne/isa/mod.rs b/src/libcretonne/isa/mod.rs
index 1d788ffff1..a43b1a5cb4 100644
--- a/src/libcretonne/isa/mod.rs
+++ b/src/libcretonne/isa/mod.rs
@@ -24,7 +24,7 @@
 //! use cretonne::isa;
 //!
 //! let shared_builder = settings::builder();
-//! let shared_flags = settings::Flags::new(shared_builder);
+//! let shared_flags = settings::Flags::new(&shared_builder);
 //!
 //! match isa::lookup("riscv") {
 //!     None => {
@@ -66,14 +66,14 @@ fn riscv_builder() -> Option<Builder> {
 /// Modify the ISA-specific settings before creating the `TargetIsa` trait object with `finish`.
 pub struct Builder {
     setup: settings::Builder,
-    constructor: fn(settings::Flags, settings::Builder) -> Box<TargetIsa>,
+    constructor: fn(settings::Flags, &settings::Builder) -> Box<TargetIsa>,
 }
 
 impl Builder {
     /// Combine the ISA-specific settings with the provided ISA-independent settings and allocate a
     /// fully configured `TargetIsa` trait object.
     pub fn finish(self, shared_flags: settings::Flags) -> Box<TargetIsa> {
-        (self.constructor)(shared_flags, self.setup)
+        (self.constructor)(shared_flags, &self.setup)
     }
 }
 
diff --git a/src/libcretonne/isa/riscv/mod.rs b/src/libcretonne/isa/riscv/mod.rs
index b1ee92a4a9..ea49358aa6 100644
--- a/src/libcretonne/isa/riscv/mod.rs
+++ b/src/libcretonne/isa/riscv/mod.rs
@@ -24,7 +24,7 @@ pub fn isa_builder() -> IsaBuilder {
 }
 
 fn isa_constructor(shared_flags: shared_settings::Flags,
-                   builder: shared_settings::Builder)
+                   builder: &shared_settings::Builder)
                    -> Box<TargetIsa> {
     let level1 = if shared_flags.is_64bit() {
         &enc_tables::LEVEL1_RV64[..]
@@ -72,7 +72,7 @@ mod tests {
     fn test_64bitenc() {
         let mut shared_builder = settings::builder();
         shared_builder.set_bool("is_64bit", true).unwrap();
-        let shared_flags = settings::Flags::new(shared_builder);
+        let shared_flags = settings::Flags::new(&shared_builder);
         let isa = isa::lookup("riscv").unwrap().finish(shared_flags);
 
         let mut dfg = DataFlowGraph::new();
@@ -119,7 +119,7 @@ mod tests {
     fn test_32bitenc() {
         let mut shared_builder = settings::builder();
         shared_builder.set_bool("is_64bit", false).unwrap();
-        let shared_flags = settings::Flags::new(shared_builder);
+        let shared_flags = settings::Flags::new(&shared_builder);
         let isa = isa::lookup("riscv").unwrap().finish(shared_flags);
 
         let mut dfg = DataFlowGraph::new();
@@ -174,7 +174,7 @@ mod tests {
     fn test_rv32m() {
         let mut shared_builder = settings::builder();
         shared_builder.set_bool("is_64bit", false).unwrap();
-        let shared_flags = settings::Flags::new(shared_builder);
+        let shared_flags = settings::Flags::new(&shared_builder);
 
         // Set the supports_m stting which in turn enables the use_m predicate that unlocks
         // encodings for imul.
diff --git a/src/libcretonne/isa/riscv/settings.rs b/src/libcretonne/isa/riscv/settings.rs
index ae765d9c15..57d8689ed1 100644
--- a/src/libcretonne/isa/riscv/settings.rs
+++ b/src/libcretonne/isa/riscv/settings.rs
@@ -14,9 +14,9 @@ mod tests {
 
     #[test]
     fn display_default() {
-        let shared = settings::Flags::new(settings::builder());
+        let shared = settings::Flags::new(&settings::builder());
         let b = builder();
-        let f = Flags::new(&shared, b);
+        let f = Flags::new(&shared, &b);
         assert_eq!(f.to_string(),
                    "[riscv]\n\
                     supports_m = false\n\
@@ -30,20 +30,20 @@ mod tests {
 
     #[test]
     fn predicates() {
-        let shared = settings::Flags::new(settings::builder());
+        let shared = settings::Flags::new(&settings::builder());
         let mut b = builder();
         b.set_bool("supports_f", true).unwrap();
         b.set_bool("supports_d", true).unwrap();
-        let f = Flags::new(&shared, b);
+        let f = Flags::new(&shared, &b);
         assert_eq!(f.full_float(), true);
 
         let mut sb = settings::builder();
         sb.set_bool("enable_simd", false).unwrap();
-        let shared = settings::Flags::new(sb);
+        let shared = settings::Flags::new(&sb);
         let mut b = builder();
         b.set_bool("supports_f", true).unwrap();
         b.set_bool("supports_d", true).unwrap();
-        let f = Flags::new(&shared, b);
+        let f = Flags::new(&shared, &b);
         assert_eq!(f.full_float(), false);
     }
 }
diff --git a/src/libcretonne/settings.rs b/src/libcretonne/settings.rs
index c7c0d1eb30..37d09d2ba8 100644
--- a/src/libcretonne/settings.rs
+++ b/src/libcretonne/settings.rs
@@ -16,7 +16,7 @@
 //! let mut b = settings::builder();
 //! b.set("opt_level", "fastest");
 //!
-//! let f = settings::Flags::new(b);
+//! let f = settings::Flags::new(&b);
 //! assert_eq!(f.opt_level(), settings::OptLevel::Fastest);
 //! ```
 
@@ -57,9 +57,9 @@ impl Builder {
     }
 
     /// Extract contents of builder once everything is configured.
-    pub fn finish(self, name: &str) -> Vec<u8> {
+    pub fn state_for(&self, name: &str) -> &[u8] {
         assert_eq!(name, self.template.name);
-        self.bytes
+        &self.bytes[..]
     }
 
     /// Set the value of a single bit.
@@ -256,7 +256,7 @@ mod tests {
     #[test]
     fn display_default() {
         let b = builder();
-        let f = Flags::new(b);
+        let f = Flags::new(&b);
         assert_eq!(f.to_string(),
                    "[shared]\n\
                     opt_level = \"default\"\n\
@@ -275,7 +275,7 @@ mod tests {
         assert_eq!(b.set_bool("enable_simd", true), Ok(()));
         assert_eq!(b.set_bool("enable_simd", false), Ok(()));
 
-        let f = Flags::new(b);
+        let f = Flags::new(&b);
         assert_eq!(f.enable_simd(), false);
     }
 
@@ -289,7 +289,7 @@ mod tests {
         assert_eq!(b.set("opt_level", "best"), Ok(()));
         assert_eq!(b.set("enable_simd", "0"), Ok(()));
 
-        let f = Flags::new(b);
+        let f = Flags::new(&b);
         assert_eq!(f.enable_simd(), false);
         assert_eq!(f.opt_level(), super::OptLevel::Best);
     }