diff --git a/artiq/firmware/Cargo.lock b/artiq/firmware/Cargo.lock
index f6d660460..700bc76ee 100644
--- a/artiq/firmware/Cargo.lock
+++ b/artiq/firmware/Cargo.lock
@@ -59,6 +59,11 @@ dependencies = [
  "rustc-cfg 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "compiler_builtins"
+version = "0.1.0"
+source = "git+https://github.com/m-labs/compiler-builtins?rev=97916b1#97916b17ca542eac0524b8570c7d05913891a0dc"
+
 [[package]]
 name = "cslice"
 version = "0.3.0"
@@ -109,10 +114,10 @@ dependencies = [
  "board 0.0.0",
  "build_artiq 0.0.0",
  "byteorder 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "compiler_builtins 0.1.0 (git+https://github.com/m-labs/compiler-builtins?rev=97916b1)",
  "cslice 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "dyld 0.0.0",
  "proto 0.0.0",
- "rlibc 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "std_artiq 0.0.0",
 ]
 
@@ -156,11 +161,6 @@ dependencies = [
  "std_artiq 0.0.0",
 ]
 
-[[package]]
-name = "rlibc"
-version = "1.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
 [[package]]
 name = "runtime"
 version = "0.0.0"
@@ -171,7 +171,7 @@ dependencies = [
  "board 0.0.0",
  "build_artiq 0.0.0",
  "byteorder 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "compiler_builtins 0.1.0 (git+https://github.com/rust-lang-nursery/compiler-builtins?rev=631b568)",
+ "compiler_builtins 0.1.0 (git+https://github.com/m-labs/compiler-builtins?rev=97916b1)",
  "cslice 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "drtioaux 0.0.0",
  "fringe 1.1.0 (git+https://github.com/m-labs/libfringe?rev=bd23494)",
@@ -248,6 +248,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum bitflags 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b3c30d3802dfb7281680d6285f2ccdaa8c2d8fee41f93805dba5c4cf50dc23cf"
 "checksum byteorder 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "652805b7e73fada9d85e9a6682a4abd490cb52d96aeecc12e33a0de34dfd0d23"
 "checksum cc 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "a9b13a57efd6b30ecd6598ebdb302cca617930b5470647570468a65d12ef9719"
+"checksum compiler_builtins 0.1.0 (git+https://github.com/m-labs/compiler-builtins?rev=97916b1)" = "<none>"
 "checksum compiler_builtins 0.1.0 (git+https://github.com/rust-lang-nursery/compiler-builtins?rev=631b568)" = "<none>"
 "checksum cslice 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0f8cb7306107e4b10e64994de6d3274bd08996a7c1322a27b86482392f96be0a"
 "checksum fringe 1.1.0 (git+https://github.com/m-labs/libfringe?rev=bd23494)" = "<none>"
@@ -257,7 +258,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)" = "880f77541efa6e5cc74e76910c9884d9859683118839d6a1dc3b11e63512565b"
 "checksum log_buffer 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ec57723b84bbe7bdf76aa93169c9b59e67473317c6de3a83cb2a0f8ccb2aa493"
 "checksum managed 0.4.0 (git+https://github.com/m-labs/rust-managed.git?rev=629a6786a1cf1692015f464ed16c04eafa5cb8d1)" = "<none>"
-"checksum rlibc 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fc874b127765f014d792f16763a81245ab80500e2ad921ed4ee9e82481ee08fe"
 "checksum rustc-cfg 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "56a596b5718bf5e059d59a30af12f7f462a152de147aa462b70892849ee18704"
 "checksum same-file 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "d931a44fdaa43b8637009e7632a02adc4f2b2e0733c08caa4cf00e8da4a117a7"
 "checksum smoltcp 0.4.0 (git+https://github.com/m-labs/smoltcp?rev=507d2fe)" = "<none>"
diff --git a/artiq/firmware/ksupport/Cargo.toml b/artiq/firmware/ksupport/Cargo.toml
index d808e4af7..1162a848c 100644
--- a/artiq/firmware/ksupport/Cargo.toml
+++ b/artiq/firmware/ksupport/Cargo.toml
@@ -13,7 +13,6 @@ crate-type = ["staticlib"]
 build_artiq = { path = "../libbuild_artiq" }
 
 [dependencies]
-rlibc = "1.0"
 byteorder = { version = "1.0", default-features = false }
 cslice = { version = "0.3" }
 alloc_stub = { path = "../liballoc_stub" }
@@ -22,3 +21,8 @@ dyld = { path = "../libdyld" }
 board = { path = "../libboard" }
 proto = { path = "../libproto" }
 amp = { path = "../libamp" }
+
+[dependencies.compiler_builtins]
+git = "https://github.com/m-labs/compiler-builtins"
+rev = "97916b1"
+features = ["mem"]
diff --git a/artiq/firmware/ksupport/Makefile b/artiq/firmware/ksupport/Makefile
index b2ad9410c..297bad7bd 100644
--- a/artiq/firmware/ksupport/Makefile
+++ b/artiq/firmware/ksupport/Makefile
@@ -7,7 +7,6 @@ CFLAGS += \
 	-I$(MISOC_DIRECTORY)/software/include/dyld
 
 LDFLAGS += --eh-frame-hdr \
-	-L../libcompiler-rt \
 	-L../libm \
 	-L../libprintf \
 	-L../libunwind
@@ -22,7 +21,7 @@ $(RUSTOUT)/libksupport.a:
 
 ksupport.elf: $(RUSTOUT)/libksupport.a glue.o
 	$(link) -T $(KSUPPORT_DIRECTORY)/ksupport.ld \
-		-lunwind-elf -lprintf-float -lm -lcompiler-rt
+		-lunwind-elf -lprintf-float -lm
 
 %.o: $(KSUPPORT_DIRECTORY)/%.c
 	$(compile)
diff --git a/artiq/firmware/ksupport/api.rs b/artiq/firmware/ksupport/api.rs
index 1cf3ce884..d7c079243 100644
--- a/artiq/firmware/ksupport/api.rs
+++ b/artiq/firmware/ksupport/api.rs
@@ -31,8 +31,6 @@ static mut API: &'static [(&'static str, *const ())] = &[
     api!(__ltdf2),
     api!(__nedf2),
     api!(__gtdf2),
-    api!(__negsf2),
-    api!(__negdf2),
     api!(__addsf3),
     api!(__subsf3),
     api!(__mulsf3),
@@ -57,8 +55,6 @@ static mut API: &'static [(&'static str, *const ())] = &[
     api!(__fixdfsi),
     api!(__fixdfdi),
     api!(__fixunsdfsi),
-    api!(__clzsi2),
-    api!(__ctzsi2),
     api!(__udivdi3),
     api!(__umoddi3),
     api!(__moddi3),
diff --git a/artiq/firmware/ksupport/lib.rs b/artiq/firmware/ksupport/lib.rs
index 87b3cec4e..c6ec95fb2 100644
--- a/artiq/firmware/ksupport/lib.rs
+++ b/artiq/firmware/ksupport/lib.rs
@@ -1,7 +1,8 @@
-#![feature(lang_items, asm, libc, panic_unwind, unwind_attributes, global_allocator)]
+#![feature(lang_items, asm, libc, panic_unwind, unwind_attributes, global_allocator,
+           compiler_builtins_lib)]
 #![no_std]
 
-extern crate rlibc;
+extern crate compiler_builtins;
 extern crate byteorder;
 extern crate cslice;
 extern crate unwind;
diff --git a/artiq/firmware/runtime/Cargo.toml b/artiq/firmware/runtime/Cargo.toml
index 00f1ca121..468ca295d 100644
--- a/artiq/firmware/runtime/Cargo.toml
+++ b/artiq/firmware/runtime/Cargo.toml
@@ -26,8 +26,8 @@ amp = { path = "../libamp" }
 drtioaux = { path = "../libdrtioaux" }
 
 [dependencies.compiler_builtins]
-git = "https://github.com/rust-lang-nursery/compiler-builtins"
-rev = "631b568"
+git = "https://github.com/m-labs/compiler-builtins"
+rev = "97916b1"
 features = ["mem"]
 
 [dependencies.fringe]