diff --git a/go/adk/pkg/models/ollama_adk.go b/go/adk/pkg/models/ollama_adk.go
index 82f4435366..35e01c76e7 100644
--- a/go/adk/pkg/models/ollama_adk.go
+++ b/go/adk/pkg/models/ollama_adk.go
@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 	"iter"
+	"maps"
+	"slices"
 	"strings"
 
 	"github.com/google/uuid"
@@ -364,8 +366,11 @@ func convertGenaiToolsToOllama(tools []*genai.Tool) []api.Tool {
 				// Ollama requires typed properties, so we convert to map[string]any first then to api.ToolProperty.
 				if m := parametersJsonSchemaToMap(decl.ParametersJsonSchema); m != nil {
 					if props, ok := m["properties"].(map[string]any); ok {
-						for name, propAny := range props {
-							if propMap, ok := propAny.(map[string]any); ok {
+						// Sort: api.ToolPropertiesMap preserves insertion order, so
+						// ranging the map directly would emit a different property
+						// order on every call and break prompt prefix caching.
+						for _, name := range slices.Sorted(maps.Keys(props)) {
+							if propMap, ok := props[name].(map[string]any); ok {
 								prop := api.ToolProperty{}
 								if t, ok := propMap["type"].(string); ok {
 									prop.Type = api.PropertyType{t}
@@ -389,7 +394,9 @@ func convertGenaiToolsToOllama(tools []*genai.Tool) []api.Tool {
 					}
 				}
 			} else if decl.Parameters != nil {
-				for name, schema := range decl.Parameters.Properties {
+				// Sorted for the same reason as above.
+				for _, name := range slices.Sorted(maps.Keys(decl.Parameters.Properties)) {
+					schema := decl.Parameters.Properties[name]
 					if schema == nil {
 						continue
 					}
diff --git a/go/adk/pkg/models/ollama_test.go b/go/adk/pkg/models/ollama_test.go
index 9df42d6c8d..c1174b3c32 100644
--- a/go/adk/pkg/models/ollama_test.go
+++ b/go/adk/pkg/models/ollama_test.go
@@ -2,6 +2,7 @@ package models
 
 import (
 	"reflect"
+	"slices"
 	"testing"
 
 	"google.golang.org/genai"
@@ -214,3 +215,50 @@ func TestConvertGenaiContentsToOllamaMessages(t *testing.T) {
 		})
 	}
 }
+
+// TestConvertGenaiToolsToOllamaPropertyOrderIsStable guards prompt prefix
+// caching. api.ToolPropertiesMap preserves insertion order, so if the
+// conversion ranges over the Go map of properties directly, every call emits a
+// different property order. Servers that cache on the prompt prefix then
+// re-process the whole prompt on every request.
+func TestConvertGenaiToolsToOllamaPropertyOrderIsStable(t *testing.T) {
+	props := map[string]*genai.Schema{
+		"project": {Type: genai.TypeString, Description: "project slug"},
+		"family":  {Type: genai.TypeString, Description: "change family"},
+		"bucket":  {Type: genai.TypeString, Description: "severity bucket"},
+		"since":   {Type: genai.TypeString, Description: "lower bound"},
+		"limit":   {Type: genai.TypeInteger, Description: "max rows"},
+	}
+	tools := []*genai.Tool{{
+		FunctionDeclarations: []*genai.FunctionDeclaration{{
+			Name:       "list_changes",
+			Parameters: &genai.Schema{Type: genai.TypeObject, Properties: props},
+		}},
+	}}
+
+	want := names(t, tools)
+	for i := range 100 {
+		if got := names(t, tools); !reflect.DeepEqual(got, want) {
+			t.Fatalf("property order changed between calls:\n first: %v\n call %d: %v", want, i, got)
+		}
+	}
+
+	if !slices.IsSorted(want) {
+		t.Errorf("property order is not deterministic across processes: %v", want)
+	}
+}
+
+// names returns the parameter property names of the first converted tool, in
+// the order they would be serialized.
+func names(t *testing.T, tools []*genai.Tool) []string {
+	t.Helper()
+	converted := convertGenaiToolsToOllama(tools)
+	if len(converted) != 1 {
+		t.Fatalf("expected 1 tool, got %d", len(converted))
+	}
+	var out []string
+	for name := range converted[0].Function.Parameters.Properties.All() {
+		out = append(out, name)
+	}
+	return out
+}