diff --git a/compileopts/config.go b/compileopts/config.go
index 8f815ffb..4aa8ed5e 100644
--- a/compileopts/config.go
+++ b/compileopts/config.go
@@ -211,6 +211,8 @@ func (c *Config) CFlags() []string {
 	}
 	// Always emit debug information. It is optionally stripped at link time.
 	cflags = append(cflags, "-g")
+	// Use the same optimization level as TinyGo.
+	cflags = append(cflags, "-O"+c.Options.Opt)
 	return cflags
 }
 
diff --git a/targets/cortex-m.json b/targets/cortex-m.json
index 0021d03c..dacf2181 100644
--- a/targets/cortex-m.json
+++ b/targets/cortex-m.json
@@ -10,7 +10,6 @@
 	"automatic-stack-size": true,
 	"default-stack-size": 2048,
 	"cflags": [
-		"-Oz",
 		"-mthumb",
 		"-Werror",
 		"-fshort-enums",
diff --git a/targets/gameboy-advance.json b/targets/gameboy-advance.json
index 2eb8aaa8..e2d58159 100644
--- a/targets/gameboy-advance.json
+++ b/targets/gameboy-advance.json
@@ -10,7 +10,6 @@
 	"cflags": [
 		"--target=arm4-none-eabi",
 		"-mcpu=arm7tdmi",
-		"-Oz",
 		"-Werror",
 		"-fshort-enums",
 		"-fomit-frame-pointer",
diff --git a/targets/riscv.json b/targets/riscv.json
index 1ccf123a..4b78db60 100644
--- a/targets/riscv.json
+++ b/targets/riscv.json
@@ -7,7 +7,6 @@
 	"rtlib": "compiler-rt",
 	"libc": "picolibc",
 	"cflags": [
-		"-Os",
 		"-Werror",
 		"-fno-exceptions", "-fno-unwind-tables",
 		"-ffunction-sections", "-fdata-sections"
diff --git a/targets/wasi.json b/targets/wasi.json
index b80b77d1..fd481b65 100644
--- a/targets/wasi.json
+++ b/targets/wasi.json
@@ -7,8 +7,7 @@
 	"libc":          "wasi-libc",
 	"cflags": [
 		"--target=wasm32--wasi",
-		"--sysroot={root}/lib/wasi-libc/sysroot",
-		"-Oz"
+		"--sysroot={root}/lib/wasi-libc/sysroot"
 	],
 	"ldflags": [
 		"--allow-undefined",
diff --git a/targets/wasm.json b/targets/wasm.json
index eb03eb8c..083b6230 100644
--- a/targets/wasm.json
+++ b/targets/wasm.json
@@ -7,8 +7,7 @@
 	"libc":          "wasi-libc",
 	"cflags": [
 		"--target=wasm32--wasi",
-		"--sysroot={root}/lib/wasi-libc/sysroot",
-		"-Oz"
+		"--sysroot={root}/lib/wasi-libc/sysroot"
 	],
 	"ldflags": [
 		"--allow-undefined",
diff --git a/targets/xtensa.json b/targets/xtensa.json
index 6ebfc4e9..7fa24f5b 100644
--- a/targets/xtensa.json
+++ b/targets/xtensa.json
@@ -7,7 +7,6 @@
 	"scheduler": "none",
 	"cflags": [
 		"--target=xtensa",
-		"-Oz",
 		"-Werror",
 		"-fshort-enums",
 		"-Wno-macro-redefined",