diff --git a/simgear/math/simd.hxx b/simgear/math/simd.hxx
index b5dc6e91..e0a20120 100644
--- a/simgear/math/simd.hxx
+++ b/simgear/math/simd.hxx
@@ -211,8 +211,9 @@ public:
         *this += r.v4();
         return *this;
     }
-    inline simd4_t<T,N>& operator+=(const simd4_t<T,N>& v) {
-        for (int i=0; i<N; i++) {
+    template<int M>
+    inline simd4_t<T,N>& operator+=(const simd4_t<T,M>& v) {
+        for (int i=0; i<M; i++) {
            vec[i] += v[i];
         }
         return *this;
diff --git a/simgear/math/simd4x4.hxx b/simgear/math/simd4x4.hxx
index fab1f0ee..5d22a864 100644
--- a/simgear/math/simd4x4.hxx
+++ b/simgear/math/simd4x4.hxx
@@ -158,8 +158,7 @@ public:
         m -= *this; return m;
     }
 
-    template<typename S>
-    inline simd4x4_t<T,N> operator*(S s) {
+    inline simd4x4_t<T,N> operator*(T s) {
         simd4x4_t<T,N> r(*this);
         r *= s;
         return r;
@@ -168,8 +167,7 @@ public:
         m *= *this; return m;
     }
 
-    template<typename S>
-    inline simd4x4_t<T,N> operator/(S s) {
+    inline simd4x4_t<T,N> operator/(T s) {
         simd4x4_t<T,N> r(*this);
         r *= (1/T(s));
         return r;
@@ -219,8 +217,7 @@ public:
         return *this;
     }
 
-    template<typename S>
-    inline simd4x4_t<T,N>& operator/=(S s) {
+    inline simd4x4_t<T,N>& operator/=(T s) {
         return operator*=(1/T(s));
     }
 };