diff --git a/Makefile.in b/Makefile.in
index 5683eb7ba06..48b211167cf 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -65,6 +65,7 @@
 #
 #   * `VERBOSE=1` - Print all commands. Use this to see what's going on.
 #   * `RUSTFLAGS=...` - Add compiler flags to all `rustc` invocations
+#   * `JEMALLOC_FLAGS=...` - Pass flags to jemalloc's configure script
 #
 #   * `TESTNAME=...` - Specify the name of tests to run
 #   * `CHECK_IGNORED=1` - Run normally-ignored tests
diff --git a/mk/main.mk b/mk/main.mk
index 2bdfc1bafd7..3d5d0b441f1 100644
--- a/mk/main.mk
+++ b/mk/main.mk
@@ -90,15 +90,19 @@ endif
 CFG_RUSTC_FLAGS := $(RUSTFLAGS)
 CFG_GCCISH_CFLAGS :=
 CFG_GCCISH_LINK_FLAGS :=
+CFG_JEMALLOC_FLAGS :=
 
 ifdef CFG_DISABLE_OPTIMIZE
   $(info cfg: disabling rustc optimization (CFG_DISABLE_OPTIMIZE))
   CFG_RUSTC_FLAGS +=
+  CFG_JEMALLOC_FLAGS += --enable-debug
 else
   # The rtopt cfg turns off runtime sanity checks
   CFG_RUSTC_FLAGS += -O --cfg rtopt
 endif
 
+CFG_JEMALLOC_FLAGS += $(JEMALLOC_FLAGS)
+
 ifdef CFG_DISABLE_DEBUG
   CFG_RUSTC_FLAGS += --cfg ndebug
   CFG_GCCISH_CFLAGS += -DRUST_NDEBUG
diff --git a/mk/rt.mk b/mk/rt.mk
index 13ed4abb438..216abcf5f3e 100644
--- a/mk/rt.mk
+++ b/mk/rt.mk
@@ -301,7 +301,7 @@ JEMALLOC_LOCAL_$(1) := $$(JEMALLOC_BUILD_DIR_$(1))/lib/$$(JEMALLOC_REAL_NAME_$(1
 $$(JEMALLOC_LOCAL_$(1)): $$(JEMALLOC_DEPS) $$(MKFILE_DEPS)
 	@$$(call E, make: jemalloc)
 	cd "$$(JEMALLOC_BUILD_DIR_$(1))"; "$(S)src/jemalloc/configure" \
-		$$(JEMALLOC_ARGS_$(1)) --with-jemalloc-prefix=je_ \
+		$$(JEMALLOC_ARGS_$(1)) --with-jemalloc-prefix=je_ $(CFG_JEMALLOC_FLAGS) \
 		--build=$(CFG_BUILD) --host=$(1) \
 		CC="$$(CC_$(1))" \
 		AR="$$(AR_$(1))" \