diff --git a/spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/SimpleFunctionRegistry.java b/spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/SimpleFunctionRegistry.java
index d1d5c9593..1d7d0e2c6 100644
--- a/spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/SimpleFunctionRegistry.java
+++ b/spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/SimpleFunctionRegistry.java
@@ -544,6 +544,12 @@ public class SimpleFunctionRegistry implements FunctionRegistry, FunctionInspect
 
 			Object invocationResult = null;
 			if (this.target instanceof Function) {
+				if (FunctionTypeUtils.isMono(FunctionTypeUtils.getInputType(this.getFunctionType(), 0)) && input instanceof Flux) {
+					input = Mono.from((Publisher) input);
+				}
+				else if (FunctionTypeUtils.isFlux(FunctionTypeUtils.getInputType(this.getFunctionType(), 0)) && input instanceof Mono) {
+					input = Flux.from((Publisher) input);
+				}
 				invocationResult = ((Function) target).apply(input);
 			}
 			else if (this.target instanceof Supplier) {
diff --git a/spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/BeanFactoryAwareFunctionRegistryTests.java b/spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/BeanFactoryAwareFunctionRegistryTests.java
index 827115fe5..c23e5c2a1 100644
--- a/spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/BeanFactoryAwareFunctionRegistryTests.java
+++ b/spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/BeanFactoryAwareFunctionRegistryTests.java
@@ -32,6 +32,7 @@ import java.util.stream.Collectors;
 import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Test;
+import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.util.function.Tuple2;
@@ -519,6 +520,17 @@ public class BeanFactoryAwareFunctionRegistryTests {
 		assertThat(((Person) config.consumerInputRef.get()).getName()).isEqualTo("Ricky");
 	}
 
+	@Test
+	public void testGH_609() {
+		FunctionCatalog catalog = this.configureCatalog(SampleFunctionConfiguration.class);
+		Function<Publisher<String>, Publisher<String>> f = catalog.lookup("monoToMono");
+		Mono<String> result = (Mono<String>) f.apply(Mono.just("hello"));
+		assertThat(result.block()).isEqualTo("hello");
+
+		result = (Mono<String>) f.apply(Flux.just("hello"));
+		assertThat(result.block()).isEqualTo("hello");
+	}
+
 	@EnableAutoConfiguration
 	public static class PojoToMessageFunctionCompositionConfiguration {