diff --git a/libs/ardour/plugin_manager.cc b/libs/ardour/plugin_manager.cc
index e88541317c..37eb61ef3b 100644
--- a/libs/ardour/plugin_manager.cc
+++ b/libs/ardour/plugin_manager.cc
@@ -686,8 +686,7 @@ PluginManager::windows_vst_refresh (bool cache_only)
 static bool windows_vst_filter (const string& str, void * /*arg*/)
 {
 	/* Not a dotfile, has a prefix before a period, suffix is "dll" */
-
-	return str[0] != '.' && (str.length() > 4 && str.find (".dll") == (str.length() - 4));
+	return str[0] != '.' && str.length() > 4 && strings_equal_ignore_case (".dll", str.substr(str.length() - 4));
 }
 
 int
diff --git a/libs/ardour/vst_info_file.cc b/libs/ardour/vst_info_file.cc
index 2d68421103..2b79f2bc77 100644
--- a/libs/ardour/vst_info_file.cc
+++ b/libs/ardour/vst_info_file.cc
@@ -351,7 +351,7 @@ vstfx_write_info_file (FILE* fp, vector<VSTInfo *> *infos)
 static bool
 vstfx_blacklist_stat (const char *dllpath, int personal)
 {
-	if (strstr (dllpath, ".so" ) == 0 && strstr(dllpath, ".dll") == 0) {
+	if (strstr (dllpath, ".so" ) == 0 && strcasestr(dllpath, ".dll") == 0) {
 		return true;
 	}
 	string const path = vstfx_blacklist_path (dllpath, personal);
@@ -435,7 +435,7 @@ vstfx_remove_infofile (const char *dllpath)
 static char *
 vstfx_infofile_stat (const char *dllpath, struct stat* statbuf, int personal)
 {
-	if (strstr (dllpath, ".so" ) == 0 && strstr(dllpath, ".dll") == 0) {
+	if (strstr (dllpath, ".so" ) == 0 && strcasestr(dllpath, ".dll") == 0) {
 		return 0;
 	}
 
@@ -494,7 +494,7 @@ vstfx_infofile_for_read (const char* dllpath)
 static FILE *
 vstfx_infofile_create (const char* dllpath, int personal)
 {
-	if (strstr (dllpath, ".so" ) == 0 && strstr(dllpath, ".dll") == 0) {
+	if (strstr (dllpath, ".so" ) == 0 && strcasestr(dllpath, ".dll") == 0) {
 		return 0;
 	}
 
diff --git a/libs/fst/scanner.cc b/libs/fst/scanner.cc
index c7cbd897db..aac1eb5d2a 100644
--- a/libs/fst/scanner.cc
+++ b/libs/fst/scanner.cc
@@ -75,7 +75,7 @@ int main (int argc, char **argv) {
 	char *dllpath = NULL;
 	if (argc == 3 && !strcmp("-f", argv[1])) {
 		dllpath = argv[2];
-		if (strstr (dllpath, ".so" ) || strstr(dllpath, ".dll")) {
+		if (strstr (dllpath, ".so" ) || strcasestr(dllpath, ".dll")) {
 			vstfx_remove_infofile(dllpath);
 			vstfx_un_blacklist(dllpath);
 		}
@@ -105,7 +105,7 @@ int main (int argc, char **argv) {
 #endif
 
 #ifdef WINDOWS_VST_SUPPORT
-	else if (strstr (dllpath, ".dll")) {
+	else if (strcasestr (dllpath, ".dll")) {
 		infos = vstfx_get_info_fst(dllpath);
 	}
 #endif