diff --git a/m4/ipopt.m4 b/m4/ipopt.m4
index 4c10733adca3bb29f2aee32416360e103b6629f7..f6bf43dfd72541329bdf6498055203fba0bee202 100644
--- a/m4/ipopt.m4
+++ b/m4/ipopt.m4
@@ -16,12 +16,12 @@ if test x$with_ipopt != xno ; then
 
 # is --with-ipopt=bla used?
 if test "x$with_ipopt" != x ; then
-	if ! test -d $with_ipopt; then
+    if ! test -d $with_ipopt; then
         AC_MSG_WARN([IPOpt directory $with_ipopt does not exist])
-	else
+    else
         # expand tilde / other stuff
-		IPOPTROOT=`cd $with_ipopt && pwd`
-	fi
+        IPOPTROOT=`cd $with_ipopt && pwd`
+    fi
 fi
 if test "x$IPOPTROOT" = x; then
     # use some default value...
@@ -54,10 +54,10 @@ if test x$HAVE_IPOPT = x1 ; then
    AC_LINK_IFELSE(AC_LANG_PROGRAM(
         [#include "coin/IpIpoptApplication.hpp"],
         [Ipopt::SmartPtr<Ipopt::IpoptApplication> app = new Ipopt::IpoptApplication();]),
-	[IPOPT_LIBS="`PKG_CONFIG_PATH=$IPOPT_LIB_PATH/pkgconfig $PKG_CONFIG --libs-only-l ipopt`"
+    [IPOPT_LIBS="`PKG_CONFIG_PATH=$IPOPT_LIB_PATH/pkgconfig $PKG_CONFIG --libs-only-l ipopt`"
          IPOPT_LDFLAGS="`PKG_CONFIG_PATH=$IPOPT_LIB_PATH/pkgconfig $PKG_CONFIG --libs-only-L ipopt`"],
-	[HAVE_IPOPT="0"
-	AC_MSG_WARN(IPOpt not found!)])
+    [HAVE_IPOPT="0"
+    AC_MSG_WARN(IPOpt not found!)])
 fi
 
 AC_LANG_POP([C++])