diff --git a/mk/main.mk b/mk/main.mk
index d45e59d9b78..a5e37641220 100644
--- a/mk/main.mk
+++ b/mk/main.mk
@@ -144,7 +144,7 @@ ifdef CFG_ENABLE_DEBUGINFO
   CFG_RUSTC_FLAGS += -g
 else ifdef CFG_ENABLE_DEBUGINFO_LINES
   $(info cfg: enabling line number debuginfo (CFG_ENABLE_DEBUGINFO_LINES))
-  CFG_RUSTC_FLAGS += -C debuginfo=1
+  CFG_RUSTC_FLAGS += -Cdebuginfo=1
 endif
 
 ifdef SAVE_TEMPS
diff --git a/mk/tests.mk b/mk/tests.mk
index fc1f4b5561a..1957c989eb0 100644
--- a/mk/tests.mk
+++ b/mk/tests.mk
@@ -632,6 +632,7 @@ endif
 # is a separate choice from whether to pass `-g` when building the
 # compiler and standard library themselves.
 CTEST_RUSTC_FLAGS := $$(subst -g,,$$(CTEST_RUSTC_FLAGS))
+CTEST_RUSTC_FLAGS := $$(subst -Cdebuginfo=1,,$$(CTEST_RUSTC_FLAGS))
 ifdef CFG_ENABLE_DEBUGINFO_TESTS
 CTEST_RUSTC_FLAGS += -g
 endif