diff --git a/src/Audio/AbstractImporter.cpp b/src/Audio/AbstractImporter.cpp
index 2e0ced0e3..28e185ebd 100644
--- a/src/Audio/AbstractImporter.cpp
+++ b/src/Audio/AbstractImporter.cpp
@@ -76,7 +76,10 @@ void AbstractImporter::doOpenFile(const std::string& filename) {
 }
 
 void AbstractImporter::close() {
-    if(isOpened()) doClose();
+    if(isOpened()) {
+        doClose();
+        CORRADE_INTERNAL_ASSERT(!isOpened());
+    }
 }
 
 Buffer::Format AbstractImporter::format() const {
diff --git a/src/Text/AbstractFont.cpp b/src/Text/AbstractFont.cpp
index aa8e054e1..560e5385e 100644
--- a/src/Text/AbstractFont.cpp
+++ b/src/Text/AbstractFont.cpp
@@ -100,7 +100,10 @@ void AbstractFont::doOpenFile(const std::string& filename, const Float size) {
 }
 
 void AbstractFont::close() {
-    if(isOpened()) doClose();
+    if(isOpened()) {
+        doClose();
+        CORRADE_INTERNAL_ASSERT(!isOpened());
+    }
 }
 
 UnsignedInt AbstractFont::glyphId(const char32_t character) {
diff --git a/src/Trade/AbstractImporter.cpp b/src/Trade/AbstractImporter.cpp
index e5e2eca1a..9d985b3dc 100644
--- a/src/Trade/AbstractImporter.cpp
+++ b/src/Trade/AbstractImporter.cpp
@@ -76,7 +76,10 @@ void AbstractImporter::doOpenFile(const std::string& filename) {
 }
 
 void AbstractImporter::close() {
-    if(isOpened()) doClose();
+    if(isOpened()) {
+        doClose();
+        CORRADE_INTERNAL_ASSERT(!isOpened());
+    }
 }
 
 Int AbstractImporter::defaultScene() {