diff --git a/firmware/application/si5351.hpp b/firmware/application/si5351.hpp
index e76a4bbb..58104f82 100644
--- a/firmware/application/si5351.hpp
+++ b/firmware/application/si5351.hpp
@@ -168,7 +168,7 @@ struct Inputs {
 	const uint32_t f_clkin;
 	const uint32_t clkin_div;
 
-	constexpr uint32_t f_clkin_out() {
+	constexpr uint32_t f_clkin_out() const {
 		return f_clkin / clkin_div;
 	}
 };
@@ -181,23 +181,23 @@ struct PLL {
 	const uint32_t b;
 	const uint32_t c;
 
-	constexpr uint32_t f_vco() {
+	constexpr uint32_t f_vco() const {
 		return f_in * (a + (float)b / (float)c);
 	}
 
-	constexpr uint32_t p1() {
+	constexpr uint32_t p1() const {
 		return 128 * a + (uint32_t)(128 * (float)b / (float)c) - 512;
 	}
 
-	constexpr uint32_t p2() {
+	constexpr uint32_t p2() const {
 		return 128 * b - c * (uint32_t)(128 * (float)b / (float)c);
 	}
 
-	constexpr uint32_t p3() {
+	constexpr uint32_t p3() const {
 		return c;
 	}
 
-	constexpr PLLReg reg(const uint8_t pll_n) {
+	constexpr PLLReg reg(const uint8_t pll_n) const {
 		return {
 			uint8_t(26 + (pll_n * 8)),
 			uint8_t((p3() >>  8) & 0xff),
@@ -224,23 +224,23 @@ struct MultisynthFractional {
 	const uint32_t c;
 	const uint32_t r_div;
 
-	constexpr uint32_t p1() {
+	constexpr uint32_t p1() const {
 		return 128 * a + (uint32_t)(128 * (float)b / (float)c) - 512;
 	}
 
-	constexpr uint32_t p2() {
+	constexpr uint32_t p2() const {
 		return 128 * b - c * (uint32_t)(128 * (float)b / (float)c);
 	}
 
-	constexpr uint32_t p3() {
+	constexpr uint32_t p3() const {
 		return c;
 	}
 
-	constexpr uint32_t f_out() {
+	constexpr uint32_t f_out() const {
 		return f_src / (a + (float)b / (float)c) / (1 << r_div);
 	}
 
-	constexpr MultisynthFractionalReg reg(const uint8_t multisynth_n) {
+	constexpr MultisynthFractionalReg reg(const uint8_t multisynth_n) const {
 		return {
 			uint8_t(42 + (multisynth_n * 8)),
 			uint8_t((p3() >> 8) & 0xFF),
@@ -260,11 +260,11 @@ struct MultisynthInteger {
 	const uint32_t a;
 	const uint32_t r_div;
 
-	constexpr uint8_t p1() {
+	constexpr uint8_t p1() const {
 		return a;
 	}
 
-	constexpr uint32_t f_out() {
+	constexpr uint32_t f_out() const {
 		return f_src / a / (1 << r_div);
 	}
 };
diff --git a/firmware/common/i2c_pp.hpp b/firmware/common/i2c_pp.hpp
index 7eabab0b..62f729e7 100644
--- a/firmware/common/i2c_pp.hpp
+++ b/firmware/common/i2c_pp.hpp
@@ -46,15 +46,15 @@ struct I2CClockConfig {
 		return 1e9 / f;
 	}
 
-	constexpr uint32_t i2c_period_count() {
+	constexpr uint32_t i2c_period_count() const {
 		return period_ns(bus_f) / period_ns(clock_source_f) + 0.5f;
 	}
 
-	constexpr uint32_t i2c_high_count() {
+	constexpr uint32_t i2c_high_count() const {
 		return high_period_ns / period_ns(clock_source_f) + 0.5f;
 	}
 
-	constexpr uint32_t i2c_low_count() {
+	constexpr uint32_t i2c_low_count() const {
 		return i2c_period_count() - i2c_high_count();
 	}
 };
diff --git a/firmware/common/memory_map.hpp b/firmware/common/memory_map.hpp
index 8b32a0cd..d8624d74 100644
--- a/firmware/common/memory_map.hpp
+++ b/firmware/common/memory_map.hpp
@@ -43,15 +43,15 @@ public:
 
 	}
 
-	constexpr uint32_t base() {
+	constexpr uint32_t base() const {
 		return base_;
 	}
 
-	constexpr uint32_t end() {
+	constexpr uint32_t end() const {
 		return base_ + size_;
 	}
 
-	constexpr size_t size() {
+	constexpr size_t size() const {
 		return size_;
 	}
 
diff --git a/firmware/common/spi_image.hpp b/firmware/common/spi_image.hpp
index e1143712..7b53fd75 100644
--- a/firmware/common/spi_image.hpp
+++ b/firmware/common/spi_image.hpp
@@ -86,7 +86,7 @@ struct region_t {
 	const size_t offset;
 	const size_t size;
 
-	constexpr const void* base() {
+	constexpr const void* base() const {
 		return reinterpret_cast<void*>(portapack::memory::map::spifi_cached.base() + offset);
 	}
 };