diff --git a/Makefile.in b/Makefile.in
index a1c276cd3d2..ebcd5c79603 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -102,9 +102,9 @@ endif
 
 ifdef CFG_ENABLE_DEBUG
   $(info cfg: enabling more debugging (CFG_ENABLE_DEBUG))
-  CFG_RUSTC_FLAGS += --cfg debug
   CFG_GCCISH_CFLAGS += -DRUST_DEBUG
 else
+  CFG_RUSTC_FLAGS += --cfg ndebug
   CFG_GCCISH_CFLAGS += -DRUST_NDEBUG
 endif
 
diff --git a/RELEASES.txt b/RELEASES.txt
index 379f64cce1a..a65c0c22142 100644
--- a/RELEASES.txt
+++ b/RELEASES.txt
@@ -10,8 +10,8 @@ Version 0.8 (October 2013)
       * Many trait inheritance bugs fixed.
       * Owned and borrowed trait objects work more reliably.
       * `copy` is no longer a keyword. It has been replaced by the `Clone` trait.
-      * rustc no longer emits code for the `debug!` macro unless it is passed
-        `--cfg debug`
+      * rustc can omit emission of code for the `debug!` macro if it is passed
+        `--cfg ndebug`
       * mod.rs is now "blessed". When loading `mod foo;`, rustc will now look
         for foo.rs, then foo/mod.rs, and will generate an error when both are
         present.
diff --git a/configure b/configure
index d7c4523d543..2b024057403 100755
--- a/configure
+++ b/configure
@@ -373,7 +373,7 @@ opt optimize-cxx 1 "build optimized C++ code"
 opt optimize-llvm 1 "build optimized LLVM"
 opt optimize-tests 1 "build tests with optimizations"
 opt llvm-assertions 1 "build LLVM with assertions"
-opt debug 0 "build with extra debug fun"
+opt debug 1 "build with extra debug fun"
 opt ratchet-bench 0 "ratchet benchmarks"
 opt fast-make 0 "use .gitmodules as timestamp for submodule deps"
 opt manage-submodules 1 "let the build manage the git submodules"
diff --git a/doc/rust.md b/doc/rust.md
index d10238c1483..e941e4f7956 100644
--- a/doc/rust.md
+++ b/doc/rust.md
@@ -3428,8 +3428,8 @@ sign (`=`) followed by the log level, from 1 to 4, inclusive. Level 1
 is the error level, 2 is warning, 3 info, and 4 debug. You can also
 use the symbolic constants `error`, `warn`, `info`, and `debug`.  Any
 logs less than or equal to the specified level will be output. If not
-specified then log level 4 is assumed.  However, debug messages are
-only available if `--cfg=debug` is passed to `rustc`.
+specified then log level 4 is assumed.  Debug messages can be omitted
+by passing `--cfg ndebug` to `rustc`.
 
 As an example, to see all the logs generated by the compiler, you would set
 `RUST_LOG` to `rustc`, which is the crate name (as specified in its `link`
diff --git a/mk/tests.mk b/mk/tests.mk
index 28bbddc787f..14b06bf047e 100644
--- a/mk/tests.mk
+++ b/mk/tests.mk
@@ -575,7 +575,7 @@ TEST_SREQ$(1)_T_$(2)_H_$(3) = \
 
 # The tests select when to use debug configuration on their own;
 # remove directive, if present, from CFG_RUSTC_FLAGS (issue #7898).
-CTEST_RUSTC_FLAGS := $$(subst --cfg debug,,$$(CFG_RUSTC_FLAGS))
+CTEST_RUSTC_FLAGS := $$(subst --cfg ndebug,,$$(CFG_RUSTC_FLAGS))
 
 # The tests can not be optimized while the rest of the compiler is optimized, so
 # filter out the optimization (if any) from rustc and then figure out if we need
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 0bee7895420..82d452bc734 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -715,7 +715,7 @@ pub fn std_macros() -> @str {
     macro_rules! warn ( ($($arg:tt)*) => (log!(2u32, $($arg)*)) )
     macro_rules! info ( ($($arg:tt)*) => (log!(3u32, $($arg)*)) )
     macro_rules! debug( ($($arg:tt)*) => (
-        if cfg!(debug) { log!(4u32, $($arg)*) }
+        if cfg!(not(ndebug)) { log!(4u32, $($arg)*) }
     ))
 
     macro_rules! log2(
@@ -730,7 +730,7 @@ pub fn std_macros() -> @str {
     macro_rules! warn2 ( ($($arg:tt)*) => (log2!(2u32, $($arg)*)) )
     macro_rules! info2 ( ($($arg:tt)*) => (log2!(3u32, $($arg)*)) )
     macro_rules! debug2( ($($arg:tt)*) => (
-        if cfg!(debug) { log2!(4u32, $($arg)*) }
+        if cfg!(not(ndebug)) { log2!(4u32, $($arg)*) }
     ))
 
     macro_rules! fail(
diff --git a/src/test/run-pass/conditional-debug-macro-off.rs b/src/test/run-pass/conditional-debug-macro-off.rs
index f40c8112e0b..1aae5ce29c0 100644
--- a/src/test/run-pass/conditional-debug-macro-off.rs
+++ b/src/test/run-pass/conditional-debug-macro-off.rs
@@ -9,9 +9,10 @@
 // except according to those terms.
 
 // xfail-fast exec-env directive doesn't work for check-fast
+// compile-flags: --cfg ndebug
 // exec-env:RUST_LOG=conditional-debug-macro-off=4
 
 fn main() {
     // only fails if debug! evaluates its argument.
     debug!({ if true { fail!() } });
-}
\ No newline at end of file
+}
diff --git a/src/test/run-pass/conditional-debug-macro-on.rs b/src/test/run-pass/conditional-debug-macro-on.rs
index 65b751a5826..2fe6d179348 100644
--- a/src/test/run-pass/conditional-debug-macro-on.rs
+++ b/src/test/run-pass/conditional-debug-macro-on.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 // xfail-fast compile-flags directive doesn't work for check-fast
-// compile-flags: --cfg debug
 // exec-env:RUST_LOG=conditional-debug-macro-on=4
 
 fn main() {
@@ -18,4 +17,4 @@ fn main() {
     debug!({ if true { return; } });
 
     fail!();
-}
\ No newline at end of file
+}