diff --git a/tools/lib/api/Makefile b/tools/lib/api/Makefile
index adba83b325d556d4b9280114905cdd3fb4b7313a..eb6e0b36bfc194771c15d66c5fe257d73cdf92de 100644
--- a/tools/lib/api/Makefile
+++ b/tools/lib/api/Makefile
@@ -17,7 +17,13 @@ MAKEFLAGS += --no-print-directory
 LIBFILE = $(OUTPUT)libapi.a
 
 CFLAGS := $(EXTRA_WARNINGS) $(EXTRA_CFLAGS)
-CFLAGS += -ggdb3 -Wall -Wextra -std=gnu99 -O6 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fPIC
+CFLAGS += -ggdb3 -Wall -Wextra -std=gnu99 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fPIC
+
+ifeq ($(CC), clang)
+  CFLAGS += -O3
+else
+  CFLAGS += -O6
+endif
 
 # Treat warnings as errors unless directed not to
 ifneq ($(WERROR),0)
diff --git a/tools/lib/subcmd/Makefile b/tools/lib/subcmd/Makefile
index 3f8cc44a0dbdad3665ad7b1f03a58a6ce3f92707..3d1c3b5b51504d3512df5825baaaeec70d6f939b 100644
--- a/tools/lib/subcmd/Makefile
+++ b/tools/lib/subcmd/Makefile
@@ -19,7 +19,13 @@ MAKEFLAGS += --no-print-directory
 LIBFILE = $(OUTPUT)libsubcmd.a
 
 CFLAGS := $(EXTRA_WARNINGS) $(EXTRA_CFLAGS)
-CFLAGS += -ggdb3 -Wall -Wextra -std=gnu99 -O6 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fPIC
+CFLAGS += -ggdb3 -Wall -Wextra -std=gnu99 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fPIC
+
+ifeq ($(CC), clang)
+  CFLAGS += -O3
+else
+  CFLAGS += -O6
+endif
 
 # Treat warnings as errors unless directed not to
 ifneq ($(WERROR),0)
diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 03cf947755b9771f7189d3acbca543f7a625ba63..2b941efadb04e34779f00c4b6348262da0fb3dd6 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -144,8 +144,12 @@ ifndef DEBUG
 endif
 
 ifeq ($(DEBUG),0)
+ifeq ($(CC), clang)
+  CFLAGS += -O3
+else
   CFLAGS += -O6
 endif
+endif
 
 ifdef PARSER_DEBUG
   PARSER_DEBUG_BISON := -t