diff --git a/configure.ac b/configure.ac
index c3c213a01..87271879c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -44,7 +44,7 @@ case $host_os in
          # in expected paths because they may conflict with system files. Ask
          # Homebrew where each one is located, then adjust paths accordingly.
          if $BREW list --versions valgrind >/dev/null; then
-           valgrind_prefix=`$BREW --prefix valgrind 2>/dev/null`
+           valgrind_prefix=$($BREW --prefix valgrind 2>/dev/null)
            VALGRIND_CPPFLAGS="-I$valgrind_prefix/include"
          fi
        else