diff --git a/include/asm-x86/io.h b/include/asm-x86/io.h
index bf5d629b3a39..0f954dc89cb3 100644
--- a/include/asm-x86/io.h
+++ b/include/asm-x86/io.h
@@ -21,7 +21,7 @@ extern void __iomem *fix_ioremap(unsigned idx, unsigned long phys);
 
 #define build_mmio_read(name, size, type, reg, barrier) \
 static inline type name(const volatile void __iomem *addr) \
-{ type ret; asm volatile("mov" size " %1,%0":"=" reg (ret) \
+{ type ret; asm volatile("mov" size " %1,%0":reg (ret) \
 :"m" (*(volatile type __force *)addr) barrier); return ret; }
 
 #define build_mmio_write(name, size, type, reg, barrier) \
@@ -29,13 +29,13 @@ static inline void name(type val, volatile void __iomem *addr) \
 { asm volatile("mov" size " %0,%1": :reg (val), \
 "m" (*(volatile type __force *)addr) barrier); }
 
-build_mmio_read(readb, "b", unsigned char, "q", :"memory")
-build_mmio_read(readw, "w", unsigned short, "r", :"memory")
-build_mmio_read(readl, "l", unsigned int, "r", :"memory")
+build_mmio_read(readb, "b", unsigned char, "=q", :"memory")
+build_mmio_read(readw, "w", unsigned short, "=r", :"memory")
+build_mmio_read(readl, "l", unsigned int, "=r", :"memory")
 
-build_mmio_read(__readb, "b", unsigned char, "q", )
-build_mmio_read(__readw, "w", unsigned short, "r", )
-build_mmio_read(__readl, "l", unsigned int, "r", )
+build_mmio_read(__readb, "b", unsigned char, "=q", )
+build_mmio_read(__readw, "w", unsigned short, "=r", )
+build_mmio_read(__readl, "l", unsigned int, "=r", )
 
 build_mmio_write(writeb, "b", unsigned char, "q", :"memory")
 build_mmio_write(writew, "w", unsigned short, "r", :"memory")
@@ -59,8 +59,8 @@ build_mmio_write(__writel, "l", unsigned int, "r", )
 #define mmiowb() barrier()
 
 #ifdef CONFIG_X86_64
-build_mmio_read(readq, "q", unsigned long, "r", :"memory")
-build_mmio_read(__readq, "q", unsigned long, "r", )
+build_mmio_read(readq, "q", unsigned long, "=r", :"memory")
+build_mmio_read(__readq, "q", unsigned long, "=r", )
 build_mmio_write(writeq, "q", unsigned long, "r", :"memory")
 build_mmio_write(__writeq, "q", unsigned long, "r", )