diff --git a/samples/exiv2json.cpp b/samples/exiv2json.cpp
index 4f43280d..07707219 100644
--- a/samples/exiv2json.cpp
+++ b/samples/exiv2json.cpp
@@ -347,11 +347,11 @@ int main(int argc, char* const argv[])
         Jzon::Writer writer(root, Jzon::StandardFormat);
         writer.Write();
         std::cout << writer.GetResult() << std::endl;
-        return 0;
+        return EXIT_SUCCESS;
     }
 
     catch (Exiv2::Error& e) {
         std::cout << "Caught Exiv2 exception '" << e.what() << "'\n";
-        return -1;
+        return EXIT_FAILURE;
     }
 }
diff --git a/test/data/issue_94_poc3.pgf b/test/data/issue_94_poc3.pgf
new file mode 100644
index 00000000..d4747083
Binary files /dev/null and b/test/data/issue_94_poc3.pgf differ
diff --git a/tests/bugfixes/github/test_issue_984.py b/tests/bugfixes/github/test_issue_984.py
new file mode 100644
index 00000000..fb7b8393
--- /dev/null
+++ b/tests/bugfixes/github/test_issue_984.py
@@ -0,0 +1,20 @@
+import system_tests
+
+
+class XMPMetaDeleteNamespace(
+        metaclass=system_tests.CaseMeta):
+    """
+    Regression test for the bug described in:
+    https://github.com/Exiv2/exiv2/issues/984
+    """
+    url = "https://github.com/Exiv2/exiv2/issues/984"
+
+    filename = system_tests.path(
+        "$data_path/issue_94_poc3.pgf"
+    )
+    commands = ["$exiv2json $filename"]
+    stdout = ["""Caught Exiv2 exception 'XMP Toolkit error 9: Fatal namespace map problem'
+"""]
+    stderr = ["""Warning: Removing 54 characters from the beginning of the XMP packet
+"""]
+    retval = [1]
diff --git a/xmpsdk/src/XMPMeta.cpp b/xmpsdk/src/XMPMeta.cpp
index b3af7429..30ff4a5a 100644
--- a/xmpsdk/src/XMPMeta.cpp
+++ b/xmpsdk/src/XMPMeta.cpp
@@ -1128,7 +1128,7 @@ XMPMeta::DeleteNamespace ( XMP_StringPtr namespaceURI )
 	if ( uriPos == sNamespaceURIToPrefixMap->end() ) return;
 
 	XMP_StringMapPos prefixPos = sNamespacePrefixToURIMap->find ( uriPos->second );
-	XMP_Assert ( prefixPos != sNamespacePrefixToURIMap->end() );
+	if ( prefixPos == sNamespacePrefixToURIMap->end() ) return;
 	
 	sNamespaceURIToPrefixMap->erase ( uriPos );
 	sNamespacePrefixToURIMap->erase ( prefixPos );