diff --git a/include/common/aarch32/el3_common_macros.S b/include/common/aarch32/el3_common_macros.S
index 463a080..f6b7527 100644
--- a/include/common/aarch32/el3_common_macros.S
+++ b/include/common/aarch32/el3_common_macros.S
@@ -98,6 +98,11 @@
 	orr	r0, r0, #FPEXC_EN_BIT
 	vmsr	FPEXC, r0
 	isb
+
+	/* Disable secure self-hosted invasive debug. */
+	ldr	r0, =SDCR_DEF_VAL
+	stcopr	r0, SDCR
+
 	.endm
 
 /* -----------------------------------------------------------------------------
diff --git a/include/common/aarch64/el3_common_macros.S b/include/common/aarch64/el3_common_macros.S
index cbfa6ee..d8fd625 100644
--- a/include/common/aarch64/el3_common_macros.S
+++ b/include/common/aarch64/el3_common_macros.S
@@ -79,10 +79,11 @@
 	msr	scr_el3, x0
 
 	/* ---------------------------------------------------------------------
-	 * Reset registers that may have architecturally unknown reset values
+	 * Disable secure self-hosted invasive debug.
 	 * ---------------------------------------------------------------------
 	 */
-	msr	mdcr_el3, xzr
+	mov_imm	x0, MDCR_DEF_VAL
+	msr	mdcr_el3, x0
 
 	/* ---------------------------------------------------------------------
 	 * Enable External Aborts and SError Interrupts now that the exception
diff --git a/include/lib/aarch32/arch.h b/include/lib/aarch32/arch.h
index 170fa84..8525c7b 100644
--- a/include/lib/aarch32/arch.h
+++ b/include/lib/aarch32/arch.h
@@ -125,6 +125,14 @@
 #define SCTLR_AFE_BIT		(1 << 29)
 #define SCTLR_TE_BIT		(1 << 30)
 
+/* SDCR definitions */
+#define SDCR_SPD(x)		((x) << 14)
+#define SDCR_SPD_LEGACY		0x0
+#define SDCR_SPD_DISABLE	0x2
+#define SDCR_SPD_ENABLE		0x3
+
+#define SDCR_DEF_VAL		SDCR_SPD(SDCR_SPD_DISABLE)
+
 /* HSCTLR definitions */
 #define HSCTLR_RES1 	((1 << 29) | (1 << 28) | (1 << 23) | (1 << 22)	\
 			| (1 << 18) | (1 << 16) | (1 << 11) | (1 << 4)	\
@@ -345,6 +353,7 @@
 /* System register defines The format is: coproc, opt1, CRn, CRm, opt2 */
 #define SCR		p15, 0, c1, c1, 0
 #define SCTLR		p15, 0, c1, c0, 0
+#define SDCR		p15, 0, c1, c3, 1
 #define MPIDR		p15, 0, c0, c0, 5
 #define MIDR		p15, 0, c0, c0, 0
 #define VBAR		p15, 0, c12, c0, 0
diff --git a/include/lib/aarch64/arch.h b/include/lib/aarch64/arch.h
index 3f71824..5876ce8 100644
--- a/include/lib/aarch64/arch.h
+++ b/include/lib/aarch64/arch.h
@@ -195,6 +195,15 @@
 #define SCR_NS_BIT		(1 << 0)
 #define SCR_VALID_BIT_MASK	0x2f8f
 
+/* MDCR definitions */
+#define MDCR_SPD32(x)		((x) << 14)
+#define MDCR_SPD32_LEGACY	0x0
+#define MDCR_SPD32_DISABLE	0x2
+#define MDCR_SPD32_ENABLE	0x3
+#define MDCR_SDD_BIT		(1 << 16)
+
+#define MDCR_DEF_VAL		(MDCR_SDD_BIT | MDCR_SPD32(MDCR_SPD32_DISABLE))
+
 /* HCR definitions */
 #define HCR_RW_BIT		(1ull << 31)
 #define HCR_AMO_BIT		(1 << 5)