diff --git a/include/bl31/bl31.h b/include/bl31/bl31.h
index 33e4ece..96867b0 100644
--- a/include/bl31/bl31.h
+++ b/include/bl31/bl31.h
@@ -40,7 +40,7 @@
 void bl31_next_el_arch_setup(uint32_t security_state);
 void bl31_set_next_image_type(uint32_t type);
 uint32_t bl31_get_next_image_type(void);
-void bl31_prepare_next_image_entry();
+void bl31_prepare_next_image_entry(void);
 void bl31_register_bl32_init(int32_t (*)(void));
 
 #endif /* __BL31_H__ */
diff --git a/include/bl31/runtime_svc.h b/include/bl31/runtime_svc.h
index f3543d4..2d84986 100644
--- a/include/bl31/runtime_svc.h
+++ b/include/bl31/runtime_svc.h
@@ -264,7 +264,7 @@
 /*******************************************************************************
  * Function & variable prototypes
  ******************************************************************************/
-void runtime_svc_init();
+void runtime_svc_init(void);
 extern uint64_t __RT_SVC_DESCS_START__;
 extern uint64_t __RT_SVC_DESCS_END__;
 void init_crash_reporting(void);
diff --git a/include/lib/aarch64/arch_helpers.h b/include/lib/aarch64/arch_helpers.h
index 673e897..6ba37c2 100644
--- a/include/lib/aarch64/arch_helpers.h
+++ b/include/lib/aarch64/arch_helpers.h
@@ -85,14 +85,14 @@
 
 /* Define function for simple system instruction */
 #define DEFINE_SYSOP_FUNC(_op)				\
-static inline void _op()				\
+static inline void _op(void)				\
 {							\
 	__asm__ (#_op);					\
 }
 
 /* Define function for system instruction with type specifier */
 #define DEFINE_SYSOP_TYPE_FUNC(_op, _type)		\
-static inline void _op ## _type()			\
+static inline void _op ## _type(void)			\
 {							\
 	__asm__ (#_op " " #_type);			\
 }
diff --git a/include/plat/common/platform.h b/include/plat/common/platform.h
index 714f6e0..c087dc6 100644
--- a/include/plat/common/platform.h
+++ b/include/plat/common/platform.h
@@ -165,7 +165,7 @@
 /*******************************************************************************
  * Optional BL3-1 functions (may be overridden)
  ******************************************************************************/
-void bl31_plat_enable_mmu();
+void bl31_plat_enable_mmu(void);
 
 /*******************************************************************************
  * Mandatory BL3-2 functions (only if platform contains a BL3-2)
@@ -175,6 +175,6 @@
 /*******************************************************************************
  * Optional BL3-2 functions (may be overridden)
  ******************************************************************************/
-void bl32_plat_enable_mmu();
+void bl32_plat_enable_mmu(void);
 
 #endif /* __PLATFORM_H__ */