diff --git a/src/main/java/org/codejive/properties/Properties.java b/src/main/java/org/codejive/properties/Properties.java
index f887417..f1604aa 100644
--- a/src/main/java/org/codejive/properties/Properties.java
+++ b/src/main/java/org/codejive/properties/Properties.java
@@ -441,9 +441,16 @@ public String putRaw(String rawKey, String rawValue) {
     private void replaceValue(String key, String rawValue, String value) {
         Cursor pos = indexOf(key);
         validate(pos.nextIf(PropertiesParser.Type.KEY), pos);
-        validate(pos.nextIf(PropertiesParser.Type.SEPARATOR), pos);
-        validate(pos.isType(PropertiesParser.Type.VALUE), pos);
-        pos.replace(new PropertiesParser.Token(PropertiesParser.Type.VALUE, rawValue, value));
+        if (!pos.isType(PropertiesParser.Type.SEPARATOR)) {
+            pos.add(new PropertiesParser.Token(PropertiesParser.Type.SEPARATOR, "="));
+        } else {
+            pos.next();
+        }
+        if (pos.isType(PropertiesParser.Type.VALUE)) {
+            pos.replace(new PropertiesParser.Token(PropertiesParser.Type.VALUE, rawValue, value));
+        } else {
+            pos.add(new PropertiesParser.Token(PropertiesParser.Type.VALUE, rawValue, value));
+        }
     }
 
     // Add new tokens to the end of the list of tokens
diff --git a/src/test/java/org/codejive/properties/TestProperties.java b/src/test/java/org/codejive/properties/TestProperties.java
index f5fa348..d69915c 100644
--- a/src/test/java/org/codejive/properties/TestProperties.java
+++ b/src/test/java/org/codejive/properties/TestProperties.java
@@ -1159,6 +1159,21 @@ void testPutCrLf() throws IOException {
         assertThat(sw.toString()).isEqualTo(expected);
     }
 
+    @Test
+    void testPutReplaceMissingSepOrValue() throws IOException, URISyntaxException {
+        final String given = "key1=val1\n" + "key2=\n" + "key3";
+        final String expected = "key1=value1\n" + "key2=value2\n" + "key3=value3";
+
+        Properties p = Properties.loadProperties(new StringReader(given));
+        p.put("key1", "value1");
+        p.put("key2", "value2");
+        p.put("key3", "value3");
+
+        StringWriter sw = new StringWriter();
+        p.store(sw);
+        assertThat(sw.toString()).isEqualTo(expected);
+    }
+
     private Path getResource(String name) throws URISyntaxException {
         URL resource = getClass().getResource(name);
         if (resource == null)