diff --git a/src/chipset/intel_4x0.c b/src/chipset/intel_4x0.c
index 2a4f62dc9..fa0ed301a 100644
--- a/src/chipset/intel_4x0.c
+++ b/src/chipset/intel_4x0.c
@@ -1540,6 +1540,15 @@ static void
 	cpu_update_waitstates();
     }
 
+    /* Out-of-spec PCI and AGP clocks with overclocked bus. */
+    if ((dev->type <= INTEL_440FX) && (cpu_busspeed >= 66666666))
+	cpu_set_pci_speed(cpu_busspeed / 2);
+
+    if ((dev->type >= INTEL_440BX) && (cpu_busspeed >= 100000000))
+	cpu_set_agp_speed(cpu_busspeed / 1.5);
+    else if (dev->type >= INTEL_440LX)
+	cpu_set_agp_speed(cpu_busspeed);
+
     i4x0_write(regs[0x59], 0x59, 0x00, dev);
     i4x0_write(regs[0x5a], 0x5a, 0x00, dev);
     i4x0_write(regs[0x5b], 0x5b, 0x00, dev);
diff --git a/src/chipset/via_apollo.c b/src/chipset/via_apollo.c
index b9a5d77bb..f780ba142 100644
--- a/src/chipset/via_apollo.c
+++ b/src/chipset/via_apollo.c
@@ -157,19 +157,33 @@ via_apollo_setup(via_apollo_t *dev)
     if (dev->id >= VIA_691)
 	dev->pci_conf[0x67] = 0xec;	/* DRAM Timing for Banks 6, 7 */
     if (dev->id >= VIA_693A) {
-	if (cpu_busspeed < 95000000)
-		dev->pci_conf[0x68] |= 0x00; /* 66 MHz */
-	else if (cpu_busspeed < 124000000)
-		dev->pci_conf[0x68] |= 0x01; /* 100 MHz */
-	else
-		dev->pci_conf[0x68] |= (dev->id == VIA_8601) ? 0x03 : 0x02; /* 133 MHz */
+	if (cpu_busspeed < 95000000) { /* 66 MHz */
+		cpu_set_pci_speed(cpu_busspeed / 2);
+		cpu_set_agp_speed(cpu_busspeed);
+		dev->pci_conf[0x68] |= 0x00;
+	} else if (cpu_busspeed < 124000000) { /* 100 MHz */
+		cpu_set_pci_speed(cpu_busspeed / 3);
+		cpu_set_agp_speed(cpu_busspeed / 1.5);
+		dev->pci_conf[0x68] |= 0x01;
+	} else { /* 133 MHz */
+		cpu_set_pci_speed(cpu_busspeed / 4);
+		cpu_set_agp_speed(cpu_busspeed / 2);
+		dev->pci_conf[0x68] |= (dev->id == VIA_8601) ? 0x03 : 0x02;
+	}
     } else if (dev->id >= VIA_598) {
-	if (cpu_busspeed < 75000000)
-		dev->pci_conf[0x68] |= 0x00; /* 66 MHz */
-	else if (cpu_busspeed < 100000000)
-		dev->pci_conf[0x68] |= (dev->id >= VIA_691) ? 0x00 : 0x03; /* 75/83 MHz (66 MHz on 691) */
-	else
-		dev->pci_conf[0x68] |= 0x01; /* 100 MHz */
+	if (cpu_busspeed < ((dev->id >= VIA_691) ? 100000000 : 75000000)) { /* 66 MHz */
+		cpu_set_pci_speed(cpu_busspeed / 2);
+		cpu_set_agp_speed(cpu_busspeed);
+		dev->pci_conf[0x68] |= 0x00;
+	} else if (cpu_busspeed < 100000000) { /* 75/83 MHz (not available on 691) */
+		cpu_set_pci_speed(cpu_busspeed / 2.5);
+		cpu_set_agp_speed(cpu_busspeed / 1.25);
+		dev->pci_conf[0x68] |= 0x03;
+	} else { /* 100 MHz */
+		cpu_set_pci_speed(cpu_busspeed / 3);
+		cpu_set_agp_speed(cpu_busspeed / 1.5);
+		dev->pci_conf[0x68] |= 0x01;
+	}
     }
     dev->pci_conf[0x6b] = 0x01;