diff --git a/m4/ax_blas.m4 b/m4/ax_blas.m4
index e4f96cbe..7e6fd549 100644
--- a/m4/ax_blas.m4
+++ b/m4/ax_blas.m4
@@ -98,6 +98,11 @@ if test "x$BLAS_LIBS" != x; then
 fi
 fi
 
+# don't probe if explicitly defined; by bailing out here if the
+# argument is set, we guard against typo, incompatible libs. etc.
+# being inadvertedly overrided by another (random) implementation
+if test "x$with_blas" == x; then
+
 # BLAS linked to by default?  (happens on some supercomputers)
 if test $ax_blas_ok = no; then
 	save_LIBS="$LIBS"; LIBS="$LIBS"
@@ -186,6 +191,9 @@ if test $ax_blas_ok = no; then
 	AC_CHECK_LIB(blas, $sgemm, [ax_blas_ok=yes; BLAS_LIBS="-lblas"])
 fi
 
+# end of guard against automatic overriding explicit definitions
+fi
+
 AC_SUBST(BLAS_LIBS)
 
 LIBS="$ax_blas_save_LIBS"
diff --git a/m4/ax_lapack.m4 b/m4/ax_lapack.m4
index 6aa16aaf..ad188f9e 100644
--- a/m4/ax_lapack.m4
+++ b/m4/ax_lapack.m4
@@ -101,6 +101,11 @@ if test "x$LAPACK_LIBS" != x; then
         fi
 fi
 
+# don't probe if explicitly defined; by bailing out here if the
+# argument is set, we guard against typo, incompatible libs. etc.
+# being inadvertedly overrided by another (random) implementation
+if test "x$with_lapack" == x; then
+
 # LAPACK linked to by default?  (is sometimes included in BLAS lib)
 if test $ax_lapack_ok = no; then
         save_LIBS="$LIBS"; LIBS="$LIBS $BLAS_LIBS $FLIBS"
@@ -118,6 +123,9 @@ for lapack in lapack lapack_rs6k; do
         fi
 done
 
+# end of guard against automatic overriding explicit definitions
+fi
+
 AC_SUBST(LAPACK_LIBS)
 
 # Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND: