diff --git a/include/libopencm3/stm32/common/i2c_common_v1.h b/include/libopencm3/stm32/common/i2c_common_v1.h
index b13bffc5..e4998c61 100644
--- a/include/libopencm3/stm32/common/i2c_common_v1.h
+++ b/include/libopencm3/stm32/common/i2c_common_v1.h
@@ -362,6 +362,16 @@ specific memorymap.h header before including this header file.*/
 
 /* --- I2C function prototypes---------------------------------------------- */
 
+/**
+ * I2C speed modes.
+ */
+enum i2c_speeds {
+	i2c_speed_sm_100k,
+	i2c_speed_fm_400k,
+	i2c_speed_fmp_1m,
+	i2c_speed_unknown
+};
+
 BEGIN_DECLS
 
 void i2c_reset(uint32_t i2c);
@@ -395,6 +405,7 @@ void i2c_disable_dma(uint32_t i2c);
 void i2c_set_dma_last_transfer(uint32_t i2c);
 void i2c_clear_dma_last_transfer(uint32_t i2c);
 void i2c_transfer7(uint32_t i2c, uint8_t addr, uint8_t *w, size_t wn, uint8_t *r, size_t rn);
+void i2c_set_speed(uint32_t i2c, enum i2c_speeds speed, uint32_t clock_megahz);
 
 END_DECLS
 
diff --git a/include/libopencm3/stm32/common/i2c_common_v2.h b/include/libopencm3/stm32/common/i2c_common_v2.h
index 3012fd7f..1a9df080 100644
--- a/include/libopencm3/stm32/common/i2c_common_v2.h
+++ b/include/libopencm3/stm32/common/i2c_common_v2.h
@@ -386,6 +386,16 @@ specific memorymap.h header before including this header file.*/
 
 /* --- I2C function prototypes---------------------------------------------- */
 
+/**
+ * I2C speed modes.
+ */
+enum i2c_speeds {
+	i2c_speed_sm_100k,
+	i2c_speed_fm_400k,
+	i2c_speed_fmp_1m,
+	i2c_speed_unknown
+};
+
 BEGIN_DECLS
 
 void i2c_reset(uint32_t i2c);
@@ -431,6 +441,7 @@ void i2c_disable_rxdma(uint32_t i2c);
 void i2c_enable_txdma(uint32_t i2c);
 void i2c_disable_txdma(uint32_t i2c);
 void i2c_transfer7(uint32_t i2c, uint8_t addr, uint8_t *w, size_t wn, uint8_t *r, size_t rn);
+void i2c_set_speed(uint32_t i2c, enum i2c_speeds speed, uint32_t clock_megahz);
 
 END_DECLS
 
diff --git a/lib/stm32/common/i2c_common_v1.c b/lib/stm32/common/i2c_common_v1.c
index dff41272..2cd5785a 100644
--- a/lib/stm32/common/i2c_common_v1.c
+++ b/lib/stm32/common/i2c_common_v1.c
@@ -539,5 +539,32 @@ void i2c_transfer7(uint32_t i2c, uint8_t addr, uint8_t *w, size_t wn, uint8_t *r
 	}
 }
 
+/**
+ * Set the i2c communication speed.
+ * @param i2c peripheral, eg I2C1
+ * @param speed one of the listed speed modes @ref i2c_speeds
+ * @param clock_megahz i2c peripheral clock speed in MHz. Usually, rcc_apb1_frequency / 1e6
+ */
+void i2c_set_speed(uint32_t i2c, enum i2c_speeds speed, uint32_t clock_megahz)
+{
+	i2c_set_clock_frequency(i2c, clock_megahz);
+	switch(speed) {
+	case i2c_speed_fm_400k:
+		i2c_set_fast_mode(i2c);
+		i2c_set_ccr(i2c, clock_megahz * 5 / 6);
+		i2c_set_trise(i2c, clock_megahz + 1);
+		break;
+	default:
+		/* fall back to standard mode */
+	case i2c_speed_sm_100k:
+		i2c_set_standard_mode(i2c);
+		/* x Mhz / (100kHz * 2) */
+		i2c_set_ccr(i2c, clock_megahz * 5);
+		/* Sm mode, (100kHz) freqMhz + 1 */
+		i2c_set_trise(i2c, clock_megahz + 1);
+		break;
+	}
+}
+
 
 /**@}*/
diff --git a/lib/stm32/common/i2c_common_v2.c b/lib/stm32/common/i2c_common_v2.c
index 2dd5db8e..2116064f 100644
--- a/lib/stm32/common/i2c_common_v2.c
+++ b/lib/stm32/common/i2c_common_v2.c
@@ -436,4 +436,42 @@ void i2c_transfer7(uint32_t i2c, uint8_t addr, uint8_t *w, size_t wn, uint8_t *r
 }
 
 
+/**
+ * Set the i2c communication speed.
+ * NOTE: 1MHz mode not yet implemented!
+ * Min clock speed: 8MHz for FM, 2Mhz for SM,
+ * @param i2c peripheral, eg I2C1
+ * @param speed one of the listed speed modes @ref i2c_speeds
+ * @param clock_megahz i2c peripheral clock speed in MHz. Usually, rcc_apb1_frequency / 1e6
+ */
+void i2c_set_speed(uint32_t i2c, enum i2c_speeds speed, uint32_t clock_megahz)
+{
+	int prescaler;
+	switch(speed) {
+	case i2c_speed_fmp_1m:
+		/* FIXME - add support for this mode! */
+		break;
+	case i2c_speed_fm_400k:
+		/* target 8Mhz input, so tpresc = 125ns */
+		prescaler = clock_megahz / 8 - 1;
+		i2c_set_prescaler(i2c, prescaler);
+		i2c_set_scl_low_period(i2c, 10-1); // 1250ns
+		i2c_set_scl_high_period(i2c, 4-1); // 500ns
+		i2c_set_data_hold_time(i2c, 3); // 375ns
+		i2c_set_data_setup_time(i2c, 4-1); // 500ns
+		break;
+	default:
+		/* fall back to standard mode */
+	case i2c_speed_sm_100k:
+		/* target 4Mhz input, so tpresc = 250ns */
+		prescaler = (clock_megahz / 4) - 1;
+		i2c_set_prescaler(i2c, prescaler);
+		i2c_set_scl_low_period(i2c, 20-1); // 5usecs
+		i2c_set_scl_high_period(i2c, 16-1); // 4usecs
+		i2c_set_data_hold_time(i2c, 2); // 0.5usecs
+		i2c_set_data_setup_time(i2c, 5-1); // 1.25usecs
+		break;
+	}
+}
+
 /**@}*/