diff --git a/cmd/agent/app/builder.go b/cmd/agent/app/builder.go
index 66ab15137cb..7e14139ed6a 100644
--- a/cmd/agent/app/builder.go
+++ b/cmd/agent/app/builder.go
@@ -21,6 +21,7 @@ import (
 	"strconv"
 
 	"github.com/apache/thrift/lib/go/thrift"
+	"github.com/pkg/errors"
 	"github.com/uber/jaeger-lib/metrics"
 	"go.uber.org/zap"
 
@@ -109,7 +110,7 @@ func (b *Builder) CreateAgent(primaryProxy CollectorProxy, logger *zap.Logger, m
 	r := b.getReporter(primaryProxy)
 	processors, err := b.getProcessors(r, mFactory, logger)
 	if err != nil {
-		return nil, err
+		return nil, errors.Wrap(err, "cannot create processors")
 	}
 	server := b.HTTPServer.getHTTPServer(primaryProxy.GetManager(), mFactory)
 	return NewAgent(processors, server, logger), nil
@@ -149,7 +150,7 @@ func (b *Builder) getProcessors(rep reporter.Reporter, mFactory metrics.Factory,
 		}})
 		processor, err := cfg.GetThriftProcessor(metrics, protoFactory, handler, logger)
 		if err != nil {
-			return nil, err
+			return nil, errors.Wrap(err, "cannot create Thrift Processor")
 		}
 		retMe[idx] = processor
 	}
@@ -175,7 +176,7 @@ func (c *ProcessorConfiguration) GetThriftProcessor(
 
 	server, err := c.Server.getUDPServer(mFactory)
 	if err != nil {
-		return nil, err
+		return nil, errors.Wrap(err, "cannot create UDP Server")
 	}
 
 	return processors.NewThriftProcessor(server, c.Workers, mFactory, factory, handler, logger)
@@ -199,7 +200,7 @@ func (c *ServerConfiguration) getUDPServer(mFactory metrics.Factory) (servers.Se
 	}
 	transport, err := thriftudp.NewTUDPServerTransport(c.HostPort)
 	if err != nil {
-		return nil, err
+		return nil, errors.Wrap(err, "cannot create UDPServerTransport")
 	}
 
 	return servers.NewTBufferedServer(transport, c.QueueSize, c.MaxPacketSize, mFactory)
diff --git a/cmd/agent/app/builder_test.go b/cmd/agent/app/builder_test.go
index 864e194eae4..9a6b0e63ec6 100644
--- a/cmd/agent/app/builder_test.go
+++ b/cmd/agent/app/builder_test.go
@@ -144,7 +144,7 @@ func TestBuilderWithProcessorErrors(t *testing.T) {
 		_, err := cfg.CreateAgent(&fakeCollectorProxy{}, zap.NewNop(), metrics.NullFactory)
 		assert.Error(t, err)
 		if testCase.err != "" {
-			assert.EqualError(t, err, testCase.err)
+			assert.Contains(t, err.Error(), testCase.err)
 		} else if testCase.errContains != "" {
 			assert.True(t, strings.Contains(err.Error(), testCase.errContains), "error must contain %s", testCase.errContains)
 		}
diff --git a/cmd/agent/app/flags.go b/cmd/agent/app/flags.go
index 0ae62a8633d..34bb80d2598 100644
--- a/cmd/agent/app/flags.go
+++ b/cmd/agent/app/flags.go
@@ -66,10 +66,19 @@ func (b *Builder) InitFromViper(v *viper.Viper) *Builder {
 		p.Workers = v.GetInt(prefix + suffixWorkers)
 		p.Server.QueueSize = v.GetInt(prefix + suffixServerQueueSize)
 		p.Server.MaxPacketSize = v.GetInt(prefix + suffixServerMaxPacketSize)
-		p.Server.HostPort = v.GetString(prefix + suffixServerHostPort)
+		p.Server.HostPort = portNumToHostPort(v.GetString(prefix + suffixServerHostPort))
 		b.Processors = append(b.Processors, *p)
 	}
 
-	b.HTTPServer.HostPort = v.GetString(httpServerHostPort)
+	b.HTTPServer.HostPort = portNumToHostPort(v.GetString(httpServerHostPort))
 	return b
 }
+
+// portNumToHostPort checks if the value is a raw integer port number,
+// and converts it to ":{port}" host-port string, otherwise leaves it as is.
+func portNumToHostPort(v string) string {
+	if _, err := strconv.Atoi(v); err == nil {
+		return ":" + v
+	}
+	return v
+}