diff --git a/test/test_basic_nonfinite.cpp b/test/test_basic_nonfinite.cpp
index 1b8fc518b..324a8be67 100644
--- a/test/test_basic_nonfinite.cpp
+++ b/test/test_basic_nonfinite.cpp
@@ -35,7 +35,7 @@ and checks that can input C99 infinity and NaN too.
 #include <boost/test/auto_unit_test.hpp>
 
 #include "almost_equal.ipp"
-#include "S_.ipp"
+#include "s_.ipp"
 
 #include <boost/math/special_functions/nonfinite_num_facets.hpp>
 
diff --git a/test/test_lexical_cast.cpp b/test/test_lexical_cast.cpp
index 36807511d..cd71a6879 100644
--- a/test/test_lexical_cast.cpp
+++ b/test/test_lexical_cast.cpp
@@ -23,7 +23,7 @@
 #include <boost/math/special_functions/sign.hpp>
 #include <boost/math/special_functions/fpclassify.hpp>
 #include "almost_equal.ipp"
-#include "S_.ipp"
+#include "s_.ipp"
 
 namespace {
 
diff --git a/test/test_nonfinite_trap.cpp b/test/test_nonfinite_trap.cpp
index 628ae9e91..af468c887 100644
--- a/test/test_nonfinite_trap.cpp
+++ b/test/test_nonfinite_trap.cpp
@@ -15,7 +15,7 @@
 #include <sstream>
 #include <boost/test/auto_unit_test.hpp>
 #include "almost_equal.ipp"
-#include "S_.ipp"
+#include "s_.ipp"
 #include <boost/math/special_functions/nonfinite_num_facets.hpp>
 
 namespace {
diff --git a/test/test_signed_zero.cpp b/test/test_signed_zero.cpp
index 45186da2b..042855e97 100644
--- a/test/test_signed_zero.cpp
+++ b/test/test_signed_zero.cpp
@@ -20,7 +20,7 @@
 #include <boost/test/auto_unit_test.hpp>
 #include <boost/math/special_functions/nonfinite_num_facets.hpp>
 #include "almost_equal.ipp"
-#include "S_.ipp"
+#include "s_.ipp"
 
 namespace {