diff --git a/src/arch/mips/isa.cc b/src/arch/mips/isa.cc
index 92799ab291..7795456f15 100644
--- a/src/arch/mips/isa.cc
+++ b/src/arch/mips/isa.cc
@@ -105,7 +105,7 @@ constexpr RegClass vecElemClass(VecElemClass, VecElemClassName, 2,
         debug::IntRegs);
 constexpr RegClass vecPredRegClass(VecPredRegClass, VecPredRegClassName, 1,
         debug::IntRegs);
-constexpr RegClass matRegClass(MatRegClass, MatRegClassName, 1, debug::MatRegs);
+constexpr RegClass matRegClass(MatRegClass, MatRegClassName, 0, debug::MatRegs);
 constexpr RegClass ccRegClass(CCRegClass, CCRegClassName, 0, debug::IntRegs);
 
 } // anonymous namespace
diff --git a/src/arch/power/isa.cc b/src/arch/power/isa.cc
index ecaebade9a..50fbfd346d 100644
--- a/src/arch/power/isa.cc
+++ b/src/arch/power/isa.cc
@@ -57,7 +57,7 @@ RegClass vecRegClass(VecRegClass, VecRegClassName, 1, debug::IntRegs);
 RegClass vecElemClass(VecElemClass, VecElemClassName, 2, debug::IntRegs);
 RegClass vecPredRegClass(VecPredRegClass, VecPredRegClassName, 1,
         debug::IntRegs);
-RegClass matRegClass(MatRegClass, MatRegClassName, 1, debug::MatRegs);
+RegClass matRegClass(MatRegClass, MatRegClassName, 0, debug::MatRegs);
 RegClass ccRegClass(CCRegClass, CCRegClassName, 0, debug::IntRegs);
 
 } // anonymous namespace
diff --git a/src/arch/sparc/isa.cc b/src/arch/sparc/isa.cc
index e7807c2b0a..9bb169aefe 100644
--- a/src/arch/sparc/isa.cc
+++ b/src/arch/sparc/isa.cc
@@ -74,7 +74,7 @@ RegClass vecRegClass(VecRegClass, VecRegClassName, 1, debug::IntRegs);
 RegClass vecElemClass(VecElemClass, VecElemClassName, 2, debug::IntRegs);
 RegClass vecPredRegClass(VecPredRegClass, VecPredRegClassName, 1,
         debug::IntRegs);
-RegClass matRegClass(MatRegClass, MatRegClassName, 1, debug::MatRegs);
+RegClass matRegClass(MatRegClass, MatRegClassName, 0, debug::MatRegs);
 RegClass ccRegClass(CCRegClass, CCRegClassName, 0, debug::IntRegs);
 
 } // anonymous namespace
diff --git a/src/arch/x86/isa.cc b/src/arch/x86/isa.cc
index 7d401a6c59..dd49326a4f 100644
--- a/src/arch/x86/isa.cc
+++ b/src/arch/x86/isa.cc
@@ -147,7 +147,7 @@ RegClass vecRegClass(VecRegClass, VecRegClassName, 1, debug::IntRegs);
 RegClass vecElemClass(VecElemClass, VecElemClassName, 2, debug::IntRegs);
 RegClass vecPredRegClass(VecPredRegClass, VecPredRegClassName, 1,
         debug::IntRegs);
-RegClass matRegClass(MatRegClass, MatRegClassName, 1, debug::MatRegs);
+RegClass matRegClass(MatRegClass, MatRegClassName, 0, debug::MatRegs);
 
 } // anonymous namespace